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Showing papers on "Nucleolus published in 1969"


Journal ArticleDOI
23 May 1969-Science
TL;DR: The presence of extrachromosomal nucleoli in amphibian oocytes has permitted isolation and electron microscopic observation of the genes coding for ribosomal RNA precursor molecules.
Abstract: The presence of extrachromosomal nucleoli in amphibian oocytes has permitted isolation and electron microscopic observation of the genes coding for ribosomal RNA precursor molecules. Visualization of these genes is possible because many precursor molecules are simultaneously synthesized on each gene. Individual genes are separated by stretches of DNA that apparently are not transcribed at the time of synthesis of precursor rRNA in the extrachromosomal nucleoli.

812 citations


Journal ArticleDOI
TL;DR: The histological, ultrastructural, and biochemical changes occurring during hormone-induced cytodifferentiation of the ovalbumin-secreting glands in the chick oviduct have been studied.
Abstract: The histological, ultrastructural, and biochemical changes occurring during hormone-induced cytodifferentiation of the ovalbumin-secreting glands in the chick oviduct have been studied. Marked perivascular edema is an initial response of the immature oviduct stroma to diethylstilbestrol administration and is accompanied by an interstitial migration of mononuclear cells. Mitotic activity in the immature mucosal epithelium increases within 24 hr, and glands begin to develop on days 2–4 as budlike invaginations into the subepithelial stroma. An immediate intracellular effect of the hormone is aggregation of previously dispersed ribosomes. Ribosomal zones in the nucleolus gain prominence, and there is a progressive development of rough endoplasmic reticulum in the epithelial cells. Extensive profiles of endoplasmic reticulum are present in the gland cells by day 6. Fine apical progranules appear in the epithelial cells on day 2, and ovalbumin can be measured immunochemically by day 3 at about the same time that new species of nuclear RNA have been identified. Ovalbumin granules form within condensing vacuoles in the Golgi zone and begin to be released into the lumina of the gland acini at about day 6 of the treatment.

193 citations


Journal ArticleDOI
TL;DR: Cordycepin is an analogue of adenosine lacking the 3'-OH that prevents further elongation, thus producing a prematurely terminated RNA molecule that is unaffected by the drug.
Abstract: Cordycepin is an analogue of adenosine lacking the 39-OH When incorporated into a growing RNA molecule, cordycepin prevents further elongation, thus producing a prematurely terminated RNA molecule When HeLa cells are exposed to low concentrations of cordycepin, DNA and protein synthesis are unaffected during short exposure periods The synthesis of completed ribosomal and ribosomal-precursor (45S) RNA is significantly depressed Partially completed 45S ribosomal precursor molecules accumulate in the nucleolus 18S ribosomal RNA can be cleaved from these incomplete precursors, while 32S ribosomal precursor cannot be produced from partially snythesized 45S molecules The synthesis of transfer RNA is also reduced in the presence of cordycepin The synthesis of the nuclear heterogeneous RNA species is unaffected by the drug while the cytoplasmic heterogeneous RNA is slightly reduced

189 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that hen-specific surface antigens can be obtained by transferring the RNA made on its chromosomes to the cytoplasm of the cell in detectable amounts so long as the hen's nucleus lacks a definitive nucleolus.
Abstract: When the nucleus of a hen erythrocyte is introduced into the cytoplasm of a human or mouse cell in culture, it resumes the synthesis of RNA. The reactivated erythrocyte nucleus undergoes great enlargement, but it does not, for at least 2 or 3 days, develop nucleoli which can be discerned under the light microscope. During this period, the heterokaryon, although it may contain several active erythrocyte nuclei, does not synthesize any hen-specific surface antigens; and the hen-specific antigens introduced into the surface of the heterokaryon by the process of cell fusion are eliminated. But when, later, the erythrocyte nuclei do develop nucleoli, hen-specific antigens reappear on the surface of the heterokaryon and progressively accumulate. Before developing nucleoli, the erythrocyte nuclei synthesize little, if any, normal 28 S or 16 S RNA; but they do synthesize large amounts of the RNA which shows polydisperse sedimentation in conventional sucrose density gradients. Autoradiographic studies involving the use of a microbeam of ultraviolet light show, however, that this ‘polydisperse’ RNA is not transferred to the cytoplasm of the cell in detectable amounts so long as the erythrocyte nucleus lacks a definitive nucleolus. The inability of the erythrocyte nucleus at this stage to determine the synthesis of hen-specific surface antigens is thus attributable to the fact that it fails to transfer the RNA made on its chromosomes to the cytoplasm of the cell. When the erythrocyte nuclei develop nucleoli, however, the RNA which they make is transferred to the cytoplasm of the cell, and the synthesis of hen-specific surface antigens then begins. These experiments suggest that the nucleolus may play a decisive role in the transfer of information from nucleus to cytoplasm. The possible nature of this role is discussed.

167 citations


Journal ArticleDOI
TL;DR: Beginning at the 8-cell stage, re-incubation in nonradioactive medium results in a significant decrease in nucleolar labeling and an increase in cytoplasmic labeling suggesting that more ribosomal RNA is transferred from the nucleus to the cy toplasm at the later cleavage stages.
Abstract: Studies of cleavage stage mouse embryos are reported, with particular emphasis upon nucleolar fine structural and functional changes. Multiple fibrillar primary nucleoli are present in the early 2-cell embryo. In late 2-cell embryos, some of these nucleoli acquire a peripheral zone of granules, while others reticulate, forming nucleoli composed of fibrillo-granular cortices and fibrillar cores. The nucleoli of early 4-cell embryos are composed only of fibrils. In the middle of the 4-cell stage, some of the nucleoli acquire a peripheral granular zone, while others reticulate. The reticulated nucleoli of both the late 2-cell and 4-cell embryos can be considered, on the basis of their fine structure, to be definitive nucleoli. Early 8-cell and morula embryos usually contain only two definitive nucleoli per nucleus. 3H-5-uridine-pulsed embryos contain label localized in the nucleus, particularly over definitive nucleoli. Nucleolar labeling increases at each successive developmental stage. Beginning at the 8-cell stage, re-incubation in nonradioactive medium results in a significant decrease in nucleolar labeling and an increase in cytoplasmic labeling suggesting that more ribosomal RNA is transferred from the nucleus to the cytoplasm at the later cleavage stages.

156 citations


Journal ArticleDOI
TL;DR: Ribonucleoprotein particles containing the precursors of ribosomal RNA were extracted from L cell nucleoli and analyzed under conditions comparable to those used in the characterization of cytoplasmic ribosomes, suggesting that the precursor particles have a relatively higher ratio of protein to RNA, and that ribosome maturation involves a progressive decrease in the proportion of associated protein.
Abstract: Ribonucleoprotein (RNP) particles containing the precursors of ribosomal RNA were extracted from L cell nucleoli and analyzed under conditions comparable to those used in the characterization of cytoplasmic ribosomes. Using nucleoli from cells suitably labeled with 3H-uridine, we detected three basic RNP components, sedimenting at approximately 62S, 78S, and 110S in sucrose gradients containing magnesium. A fourth particle, sedimenting at about 95S, appears to be a dimer of the 62S and 78S components. When centrifuged in gradients containing EDTA, the 62S, 78S, and 110S particles sediment at about 55S, 65S, and 80S, respectively. RNA was extracted from RNP particles which were prepared by two cycles of zonal centrifugation. The 62S particles yielded 32S RNA and a detectable amount of 28S RNA, the 78S structures, 32S RNA and possibly some 36S RNA, and the 110S particles, a mixture of 45S, 36S, and 32S RNA's. When cells were pulsed briefly and further incubated in the presence of actinomycin D, there was a gradual shift of radioactivity from heavier to lighter particles. This observation is consistent with the scheme of maturation: 110S → 78S → 62S. The principal buoyant densities in cesium chloride of the 110S, 78S, and 62S particles are 1.465, 1.490, and 1.545, respectively. These densities are all significantly lower than 1.570, which is characteristic of the mature large subunit of cytoplasmic ribosomes, suggesting that the precursor particles have a relatively higher ratio of protein to RNA, and that ribosome maturation involves, in addition to decrease in the size of the RNA molecules, a progressive decrease in the proportion of associated protein.

111 citations


Journal ArticleDOI
TL;DR: It is concluded that partial deletions and duplications of the nucleolar organizer as well as highly variable contents of rDNA are common in the genome of these amphibians.
Abstract: In metaphase preparations from leucocytes of the toad, Bufo marinus, conspicuous secondary constrictions are present in the number 7 pair of chromosomes. These constrictions were considered to be the nucleolar organizers since they were associated with nucleoli during prophase. In 35 out of 60 individuals taken from natural populations, the homologous nucleolar organizers produced two equal-sized nucleoli and secondary constrictions (Group I animals). Pour animals (Group II) had only one very large secondary constriction in the majority of their metaphase preparations and an abnormally high frequency of cells containing one nucleolus. The remaining 21 animals (Group III) had unequal-sized constrictions in most of their metaphases but were more variable than the individuals of Groups I or II since they also had metaphases with two equal constrictions or only one constriction. The DNA from individuals of each group was hybridized with radioactive ribosomal RNA in order to correlate the size of nucleoli and constrictions with the amount of DNA (rDNA) homologous to ribosomal RNA. The two animals of Group II which were studied contained 0.056% of their genome homologous to ribosomal RNA a value considerably higher than those found for any of the animals of Groups I or III. These high values for rDNA coupled with the morphological appearance of the nucleolar homologues suggested a duplication of the nucleolar organizer in the homologue with the long constriction. The amount of rDNA in animals of Group I and III varied between 0.025 and 0.048% of the genome. Although the animals with unequal-sized constrictions (Group III) had generally lower contents of rDNA than those with equal-sized constrictions (Group I), the values overlapped between the two groups. Further evidence which correlates the size of nucleoli with the number of ribosomal RNA genes comes from studies with a “small nucleolar” mutant of the Mexican axolotl (Ambystoma mexicanum). Animals homozygous for this deletion were found to contain only 55% of the complement of rDNA present in the wild type. It is concluded that partial deletions and duplications of the nucleolar organizer as well as highly variable contents of rDNA are common in the genome of these amphibians.

102 citations



Journal ArticleDOI
TL;DR: Small oocytes in adult Rana pipiens contain a number of cytoplasmic bodies which resemble nucleoli in size, shape, and staining reactions, but these nucleolus-like bodies are, however, more finely granular than nucleoli.

80 citations


Journal ArticleDOI
TL;DR: The activation of rRNA production described in this paper is the earliest event so far detected in this system, preceding activation of DNA replication, cell replication, and dedifferentiation.
Abstract: Tissue engaged in the transformation of iris into lens, triggered by lens removal in the adult newt (Triturus viridescens), was labeled in vitro with 14C-uridine, and the sedimentation profiles of RNA synthesized by the tissue were studied in sucrose density gradients. The radioactivity in the 18S and 28S areas, which is insignificant in the normal iris, increases significantly during 2 to 10 days after lens removal, and subsequently retains a high level until the completion of lens regeneration. These data are interpreted as indicating activation of ribosomal RNA (rRNA) synthesis by lens removal, and are discussed in connection with the ultrastructural modification of the nucleoli. Further data from the radioactive profiles are consistent with the notion that the level of control of rRNA production in this system is the transcription of the rRNA precursor rather than the post-transcriptional processing of the precursor. The activation of rRNA production described in this paper is the earliest event so far detected in this system, preceding activation of DNA replication, cell replication, and dedifferentiation.

73 citations



Journal ArticleDOI
TL;DR: The results of both sets of experiments indicate that the nucleolus plays a critical role in the transfer of information from the genes to the cytoplasm of the cell.
Abstract: When a chick erythrocyte nucleus is introduced into the cytoplasm of a mutant mouse cell lacking the enzyme inosinic acid pyrophosphorylase, synthesis of the enzyme is induced. However, this synthesis does not begin until the erythrocyte nucleus develops a nucleolus. The kinetics of synthesis of the enzyme are essentially similar to those previously described for the synthesis of surface antigens specified by the chick nucleus. The results of both sets of experiments indicate that the nucleolus plays a critical role in the transfer of information from the genes to the cytoplasm of the cell.

Journal ArticleDOI
TL;DR: The evidence presented in this study indicates that Chinese hamster cells contain many nucleolus-producing sites scattered through the genome.
Abstract: Chinese hamster cell strains in the early passages in culture display wide variation in number of nucleolus-like bodies per cell, though such strains are characteristically euploid. A variety of criteria indicate that the nucleolus-like bodies are true nucleoli. Their Azure B- and fast green-staining properties indicate the presence of RNA and protein; they have typical nucleolar fine structure, including both fibrous and granular components; radioautography reveals that their patterns of uptake of uridine-(3)H into RNA are similar to those reported for nucleoli of other cell types; actinomycin D, at a level which selectively inhibits ribosomal RNA synthesis, greatly reduces their RNA synthesis and also causes segregation of fibrous and granular nucleolar components. Colchicine was used to experimentally fragment the nuclei of these cells into a number of separate karyomeres, each presumably containing some, or only one, of the chromosomes of the complement. Almost all the karyomeres contain nucleolus-like bodies which, by the same criteria applied to the multiple nucleolus-like bodies of uninuclear cells, appear to be true nucleoli. The nucleoli of individual karyomeres of the same cell often differ from each other in fine structure while the multiple nucleoli of a uninuclear cell generally resemble each other. The evidence presented in this study indicates that Chinese hamster cells contain many nucleolus-producing sites scattered through the genome.

Journal ArticleDOI
TL;DR: Antiserum to the nerve growth factor (NGF) produces a severe cytotoxic effect on sympathetic nerve cells when injected into newborn mice and incorporation experiments show that RNA synthesis is markedly reduced in the experimental ganglia already 12 h after the As injection.

Journal ArticleDOI
TL;DR: It is suggested that multiple nucleoli, or extensive and diffuse RNA granular bodies in oocyte development, are indicative of ribosomal gene amplification and single, compact nucleoli in oogenesis may indicate the lack of such amplification mechanisms.

Journal ArticleDOI
TL;DR: Lead acetate, alone or containing 2% glutaraldehyde, has been demonstrated to produce an intracellular microcrystalline precipitate of lead orthophosphate, Pb5(PO4)3OH (lead hydroxyapatite).
Abstract: Lead acetate (3–10%, pH between 4.3 and 7.0, alone or containing 2% glutaraldehyde), when used as fixative, has been demonstrated to produce an intracellular microcrystalline precipitate of lead orthophosphate, Pb5(PO4)3OH (lead hydroxyapatite). This confirms earlier work with the light microscope (6). In interphase cells the nucleoli are sharply delimited by the massive lead phosphate precipitate. Some diffuse precipitate is found in the nucleoplasm; it is always delimited by the nuclear membrane. Nucleolar localization of this orthophosphate pool is not a diffusion artifact; the pool is probably in a loosely bound state and is not retained by conventional fixatives. In maize root cells in advanced mitotic stages the lead phosphate crystals are seen distributed throughout the cytoplasm and also relatively concentrated on the late anaphase-early telophase chromosomes. This pool of inorganic phosphate anions may be involved in the mitotic cycle of chromatin condensation, and it may be partially responsible for the absence of mature ribosomes in the nucleolus through the chelation of divalent cations. It is evident that the siver-reducing component detected in the nucleoli of fixed cells (6) is a completely different substance.

Journal Article
TL;DR: It is postulated that the physical combination of the actinomycin molecules with the DNA molecules governing nucleolus synthesis may be more important than inhibition of synthesis, failure to transfer, or breakdown of newly synthesized RNA per se in producing this change.
Abstract: The effect of varying doses of actinomycin D on the nucleolar structure and RNA metabolism of hepatic parenchymal cells of the rat has been investigated. Maximal dissociation of the nucleolar components as well as maximal inhibition of RNA synthesis was seen at dose levels of the drug above 0.75 μg/gm body weight. Some gradation in the morphologic effect was seen, particularly at dose levels below 0.3 μg/gm body weight. Below this level portions of the nucleolonema persist, particularly in the periphery of the nucleolar mass, all nucleoli being affected. A dose of 0.01 μg/gm body weight produces no alteration in synthetic ability and does not produce a discernible morphologic change. Although breakdown of newly synthesized RNA is documented, and this too appears to be dose dependent, it was not possible to separate this effect from inhibition of synthesis. The exact mechanism of the morphologic alteration is still unknown. However, it is unlikely that inhibition of RNA synthesis or failure to transfer newly synthesized RNA from nucleus to cytoplasm are responsible, since regeneration of the nucleolus takes place while marked inhibition of synthesis persists and because ethionine, which produces inhibition of synthesis and prevents transfer to a similar degree, does not induce this morphologic change. Although enhanced breakdown of newly synthesized RNA remains a possible mechanism, it is postulated that the physical combination of the actinomycin molecules with the DNA molecules governing nucleolus synthesis may be more important than inhibition of synthesis, failure to transfer, or breakdown of newly synthesized RNA per se in producing this change.

Journal ArticleDOI
TL;DR: Data suggest that in cultured tobacco callus cells the formation and contraction of nucleolar vacuoles is closely related to RNA synthesis in the nucleolus.
Abstract: Previously it has been found that in tobacco callus cells nucleolar vacuoles repeatedly form and contract. In this study, nucleolar vacuoles were investigated by using radioautography, actinomycin D, and electron microscopy. It was found, from grain counts of nucleoli labeled with uridine-3H, that nucleoli containing vacuoles had more than three times as many grains/µ2 of nucleolar substance as did nucleolei without vacuoles. Treatment of tobacco callus cells with various concentrations of actinomycin D caused the percentage of cells containing nucleolar vacuoles to decrease; with the highest concentration the percentage of these cells dropped from the normal level of about 70% to less than 10%. However, after removal of actinomycin D the cells regained nucleolar vacuoles up to the control level. When radioautography was used with actinomycin D, it was found that the actinomycin D inhibited the uptake of uridine-3H, i.e. inhibited RNA synthesis, in those nucleoli which lost their nucleolar vacuoles. In addition, after removal of the cells from actinomycin D, it was found that as the cells regained nucleolar vacuoles the nucleoli also began to incorporate uridine-3H. Electron micrographs showed the nucleoli to be composed of a compact, finely fibrous central portion surrounded by a layer of dense particles 100–150 A in diameter. Nucleolar vacuoles occurred in the fibrous central portion. Dense particles similar to those in the outer layer of the nucleoli were found scattered throughout the vacuoles and in a dense layer at their outer edge. These data suggest that in cultured tobacco callus cells the formation and contraction of nucleolar vacuoles is closely related to RNA synthesis in the nucleolus.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the ultrastructural modifications caused by a thermic shock as studied by complementary methods of enzymic extraction, high resolution radioautography and biochemistry.

Journal ArticleDOI
TL;DR: Results provide support for the heat-sensitivity of nucleolar RNA synthesis which appears to be related to the integrity of the intranucleolar chromatin apparatus.

Journal ArticleDOI
TL;DR: It seems that the nurse cell nuclei of Calliphora in addition to polyploidization increase their template capacity for synthesizing rRNA in a similar way as has repeatedly been demonstrated for Amphibia.
Abstract: Origin and function of the nucleolar apparatus in nurse cell nuclei of Calliphora erythrocephala have been investigated by cytological and autoradiographic methods in some inbred lines of laboratory blowflies with well paired polytene chromosomes in the nurse cell nuclei. Besides the nucleolus at chromosome VI large numbers of multiple free nucleoli develop in the highly polyploidized nurse cells during oocyte growth. The nucleoli incorporate H3-uridine in a considerable amount producing a homogeneous and RNase-sensitive label even after short time incubation. Their capacity of RNA synthesis is independent of their spatial relationships to other nuclear components. DNA particles in the nucleoli could be identified by the Feulgen reaction and by fluorescence staining with N,N'-diethylpseudoisocya-ninchloride, which also demonstrates the existence of own templates for autonomous RNA synthesis. There are indications that the nucleolus' own DNA is produced by gene amplification beyond the level of endomitotic polyploidization in the nurse cell nuclei. A quantitative estimation of grain density in the autoradiograms shows a rigorous shift of rRNA synthesis: at least 72% of all newly synthesized macromolecular RNA in nurse cell nuclei as contrasted to 13 % of nucleolar RNA synthesis in bristle forming cells with a similar degree of polyploidy. It seems that the nurse cell nuclei of Calliphora in addition to polyploidization increase their template capacity for synthesizing rRNA in a similar way as has repeatedly been demonstrated for Amphibia. Cytological and physiological peculiarities of the nurse cells have been discussed from the viewpoint of their functional similarity to the oocyte nucleus.

Journal ArticleDOI
TL;DR: It appears that the nucleolus governs the transport not only of its own RNA, but also of the RNA which is made on other parts of the chromosomes.
Abstract: The role of the nucleolus in the transfer of RNA from nucleus to cytoplasm was examined by means of experiments in which inactivation of the whole nucleus, or of the nucleolus, was achieved by a microbeam of ultraviolet light. In heterokaryons in which a chick erythrocyte nucleus had been reactivated, no detectable amount of RNA was transferred from the reactivated nucleus to the cytoplasm of the cell until this nucleus has developed a nucleolus. In HeLa cells, inactivation of the nucleolus alone inhibited the transfer to the cytoplasm, not only of the RNA synthesized at the nucleolar site, but also of the RNA made elsewhere in the nucleus. It thus appears that the nucleolus governs the transport not only of its own RNA, but also of the RNA which is made on other parts of the chromosomes.


Journal ArticleDOI
TL;DR: Results show that the nucleolar DNA is late-replicating: it continues to be synthesized after the rest of the DNA, at the end of the S period, and the cistrons for ribosomal RNA replicate or continue to replicate after those for the other categories of RNA.

Journal ArticleDOI
TL;DR: Evidence is presented indicating that these latter zones contain coarse convoluted filaments quite similar to the loops first demonstrated by La Cour (24) and which are assumed to originate from the nucleolar-organizing chromosomes.
Abstract: The architecture of the nucleolus in Allium porum and Triticum vulgare meristematic cells has been investigated by means of digestions with various enzymes. After staining with azure B at pH4, plant nucleoli exhibit lighter regions which, under electron microscopy, correspond to the fibrillar zones characterizing these organelles. Evidence is presented indicating that these latter zones contain coarse convoluted filaments quite similar to the loops first demonstrated by La Cour (24) and which are assumed to originate from the nucleolar-organizing chromosomes. These coarse, 0.2µ wide filaments are remarkably resistant to the action of deoxyribonuclease, ribonuclease, pepsin, trypsin, or of various combinations of these enzymes and, moreover, they show insignificant incorporation of labeled thymidine even after long exposure to this DNA precursor. The clearing action of pepsin on different regions of the nucleolus lends support to the hypothesis that an amorphous material or matrix pervades the mass of this organelle. This effect is particularly striking within the particulate nucleolar zones themselves. Both ribonuclease and trypsin disorganize the RNP (ribonucleoprotein) nucleolar particles. The effect of the latter enzyme on the RNP particles is taken to indicate that they contain proteins particularly susceptible to trypsin which are essential for maintenance of their morphological integrity. Trypsin also interferes with azure B-staining of the nucleolar mass as a whole and, according to radioautographic data, extracts RNA throughout this organelle. Accordingly, the hypothesis is considered that RNA is complexed with proteins not only within the particulate nucleolar portions, as is already well known, but also in the fibrillar zones.

Journal ArticleDOI
TL;DR: The results suggest that 4 s RNA is formed from RNA of slower migration rate in chromosomes, nuclear sap and cytoplasm, and in the nucleolus, label appears immediately in the 4 s position and the profile does not show any evidence of shifts with aging in the migration properties of the fractions.

Journal ArticleDOI
TL;DR: Salivary gland nuclei of Drosophila hydei, isolated by a modification of the procedure described by Boyd et al. (9), retain their normal morphology during the isolation and subsequent incubation procedure.
Abstract: Salivary gland nuclei of Drosophila hydei, isolated by a modification of the procedure described by Boyd et al. (9), retain their normal morphology during the isolation and subsequent incubation procedure. RNA synthesis was studied in isolated nuclei by biochemical and cytological techniques. In radioautographs 70% of the nuclei displayed a distribution of labeled RNA over the nuclear constituents similar to the distribution obtained after in vivo incorporation of radioactive precursor. Chromosome puffs and the nucleoli were specifically labeled. The remaining 30% of the nuclei showed a weak to very weak incorporation of radioactive precursor. In these nuclei most of the radioautographic grains were concentrated over the nucleolus, and a few grains were randomly distributed over the chromosomes. Actinomycin D and the absence of ATP, GTP, and CTP in the medium inhibited incorporation of radioactive precursor. The radioactive product was sensitive to combined pronase and RNase digestion. Addition of E. coli RNA polymerase to the incubation medium enhanced the specific labeling over the puffed regions. The sedimentation behavior of the RNA synthesized in isolated nuclei was different from that of RNA synthesized during a 20 min pulse of radioactive precursor administered to whole glands in vivo and in vitro. Neither the steroid ecdysterone nor a temperature treatment was effective in inducing new puffs in isolated nuclei.

Journal ArticleDOI
TL;DR: The implications of this compartmentation in the intact cell are discussed in connection with (A) the availability of orthophosphate ions for the cytoplasm in those processes in which these ions affect the rate of enzymatic reactions, and (B) protein nucleic acid interactions within the nucleus and nucleolus.
Abstract: Lead acetate treatment of unfixed cells immobilizes the intracellular water-soluble, inorganic orthophosphate ions as microcrystalline lead hydroxyapatite precipitates (see reference 1). These precipitates have been analyzed with the electron microprobe. A much higher concentration of phosphorus has been found in the nucleoli of maize root tip cells fixed in lead acetate-glutaraldehyde (organic phosphorus plus inorganic orthophosphate), as compared to the nucleoli of roots fixed in glutaraldehyde alone (organic phosphorus). The concentration of the inorganic orthophosphate pool in these nucleoli is three to five times as high as the concentration of the macromolecular organic phosphate. Since nearly all of the latter is in RNA, the concentration of inorganic phosphate in the nucleolus is calculated to be roughly 0.5-0.8 M. About 30%-and up to 50%-of the total cellular inorganic phosphate is accumulated in the nucleolus since the mean concentration per cell is about 10(-2)M. In the extranucleolar part of the nucleus the mean concentration was estimated by densitometry to be roughly six times less than in the nucleolus ( 0.1 M), and appears more concentrated in the nucleoplasm than in the condensed chromatin. While there is no direct evidence for the concentration in the cytoplasm, it certainly must be much lower than the mean cellular level (i.e., < 10(-2)M) since the nucleus is about 10% of the total cell volume. The implications of this compartmentation in the intact cell are discussed in connection with (A) the availability of orthophosphate ions for the cytoplasm in those processes in which these ions affect the rate of enzymatic reactions, and (B) protein nucleic acid interactions within the nucleus and nucleolus.

Journal Article
TL;DR: Comparisons by light and electron microscopy revealed similarities between the bone marrow cells and the myeloid elements (myelocytes) of myelocytomatosis notable in the relatively low nucleus/cytoplasm ratio; very large nucleolus; and ribosome-rich cy toplasm with a grainy or “ground glass” appearance.
Abstract: Infection of avian bone marrow with strain MC29 leukosis virus in vitro resulted in infection, elaboration of virus, and growth of characteristic cells. Newly liberated virus with the infectious and neutralization properties of strain MC29 agent and growth of the cells were demonstrable 48 hr and 5–6 days respectively after infection. Studies by light and electron microscopy revealed similarities between the bone marrow cells and the myeloid elements (myelocytes) of myelocytomatosis notable in the relatively low nucleus/cytoplasm ratio; very large nucleolus; and ribosome-rich cytoplasm with a dense gray (protein) matrix and a grainy or “ground glass” appearance. Such cells differed markedly in these morphologic aspects from the myeloid cells (myeloblasts) of myeloblastic leukemia induced by BAI strain A. They also differed in their short-lived growth of 3–4 weeks when compared with myeloblast proliferation indefinitely in culture. The cells were similar to chick embryo cells morphologically altered by strain MC29 because of the characteristically large nucleolus, the high concentration of cytoplasmic ribosomes, and the slight rough endoplasmic reticulum. A notable difference was the high content of diffuse chromatin in the chick embryo cells and the reverse proportion of condensed chromatin in the myelocytes. The various aspects of strain MC29 specificity of influence on cell response are discussed.

Journal ArticleDOI
TL;DR: A comparative study was made on the pancreatic and T1 RNase digestion products of Novikoff hepatoma 28 S ribosomal RNA and its nucleolar precursors, i.e. nucleolar 28 S, 35 S, and 45 S RNA.