Showing papers in "Proceedings of the National Academy of Sciences of the United States of America in 1965"

Cytochrome f and plastocyanin: their sequence in the photosynthetic electron transport chain of Chlamydomonas reinhardi.

Abstract: The elucidation of the mechanism of photosynthetic electron transport and photosynthetic phosphorylation depends, in part, upon a knowledge of the intermediates in the photosynthetic electron transport chain and the sequence in which they act. Mutant strains of the unicellular green alga Chlamydomonas reinhardi that cannot carry out normal photosynthesis1 can aid in obtaining this knowledge. In this paper we describe results obtained with ac-206, a mutant strain that lacks cytochrome f, and ac-208, a mutant strain that lacks the copper protein, plastocyanin. Since its discovery by Katoh,2 plastocyanin has been presumed to play a role in photosynthetic electron transport. In this paper we present evidence for its participation and site of action with respect to cytochrome f in the photosynthetic electron transport chain of C. reinhardi. Organisms and Methods.-The organisms used in the experiments described below were the wild-type strain of C. reinhardi (137c), and the mutant strains ac-206 and ac-208 derived from the wild type by ultraviolet irradiation.' Cells, in the logarithmic phase of growth, were harvested either from 300-ml shake cultures or from vigorously aerated 12-liter cultures grown in the light at 250C. The growth medium differed from that previously described.4 Tris-acetate buffer, 0.02 M, pH 7.2, was used in place of both phosphate buffer and sodium acetate. Potassium phosphate buffer, 0.001 M, pH 7.0, was also added. Light was provided by daylight fluorescent lamps at an intensity of 4000 lux for cultures of wild type and ac-206, and at 2000 lux for cultures of ac-208. Chloroplast fragments for the measurement of the photoreduction of NADP and DPIP were prepared by the sonic disruption of 5-ml suspensions of cells for 30 sec according to the method described by Levine and Volkmann.5 Chloroplast fragments for the measurement of photosynthetic phosphorylation were prepared by grinding a paste of cells in purified sand. After grinding, the disrupted cells were suspended and washed in the following medium: 0.01 M potassium phosphate buffer, pH 7.5; 0.02M KCl; 0.0025M MgCl2; 0.001 M MgNa2 EDTA; and 0.001 M reduced glutathione. The separation of chloroplast fragments from whole cells was then carried out as described by Levine and Volkmann.5 The photoreduction of NADP and DPIP was measured as previously described.6 Cyclic and noncyclic photosynthetic phosphorylation were measured by the techniques described by Avron7 and Avron and Shavitt.8 Chlorophyll was determinied by a modifications of the procedure of MacKinney.10 Purified PPNR was prepared from wild-type C. reinhardi according to the procedure described by Tagawa and Arnon." Plastocyanin was measured, after partial purification, by a modification of the method of Katoh, Shiratori, and Takamiya.12 Twenty-four liters of cell culture were harvested and cells were resuspended in 0.002 M phosphate buffer, pH 7.0, to a chlorophyll concentration of about 2 mg per ml. All subsequent procedures were carried out in a cold room at 4VC. The cell suspension was added quickly, under rapid stirring, to 4 vol of acetone at about -250C (the temperature after mixing was about -10(C). The cells were then collected as quickly as possible by filtration and resuspended ill 0.01 M phosphate buffer, pH 7.0. The suspension was allowed to stand at 4VC for at least 6 hr, after which the cell debris was centrifuged out at 20,000 X g for 10 min, and the clear supernate was collected. This was then allowed to drain through a column (about 1.3 X 13 cm) of fine-meshed DEAE cellulose (Selectacel DEAE 40) equilibrated with 0.01 Al phosphate buffer, pH 7.0. The column was then eluted with 20 ml of 0.05 M phosphate buffer, pH 7.0, followed by 30 ml of 0.05 M phosphate buffer with 0.15 Al KCl. The column effluejit was collected in 5-ml fractions. The plastocyanin was nearly always confined to the first 20 ml of

Catabolic repression of bacterial sporulation.

Abstract: 23 Collier, J. R., Exptl. Cell Res., 21, 126 (1960). 24 Gross, P. R., and G. H. Cousineau, Exptl. Cell Res., 33, 368 (1964). 25 Denis, H., Develop. Biol., 9, 450 (1964). 26 Brachet, J., and H. Denis, Nature, 198, 205 (1963). 27 Harvey, E. B., Biol. Bull., 79, 166 (1940). 28 Collier, J. R., Acta Embryol. Morphol. Exptl., 4, 70 (1961). 29 Davidson, E. H., V. G. Allfrey, and A. E. Mirsky, these PROCEEDINGS, 49, 53 (1963). 30 Collier, J. R., Exptl. Cell Res., 24, 320 (1961). 31 Novikoff, A. B., Biol. Bull., 74, 211 (1938). 32 Curtis, A. S. G., J. Embryol. Exptl. Morphol., 10, 410 (1962). 33 Fankhauser, G., Ann. N.Y. Acad. Sci., 49, 684 (1948). 34 Conklin, E. G., J. Acad. Nat. Sci. Phila., 2nd ser., 13, 1 (1905). 35 Huettner, A. F., J. Morphol., 37, 385 (1923).

Mechanism of action of penicillins: a proposal based on their structural similarity to acyl-D-alanyl-D-alanine.

Abstract: 4Crawford, L. V., R. Dulbecco, M. Fried, L. Montagnier, and M. G. P. Stoker, these PNoCEEDINGS, 52, 148 (1964). Bourgaux, P., D. Bourgaux-Ramoisy, and M. G. P. Stoker, Virology, 25, 364 (1965). 6Black, P. H., and W. P. Rowe, these PROCEEDINGS, 50, 606 (1963). 7Diderholm, H., B. Stenkvist, J. Ponten, and T. Wesslen, Exptl. Cell Res., 37, 452 (1965). 8 Black, P. H., and W. P. Rowe, J. Nati. Cancer Inst., 32, 253 (1964). 9 Hopps, H. E., B. C. Bernheim, A. Nisalak, J. H. Tjio, and J. E. Smadel, J. Immunol., 91, 416 (1963). 10Black, P. H., E. M. Crawford, and L. V. Crawford, Virology, 24, 381 (1964). 11 Weil, R., Virology, 14 (1961). 12 Black, P. H., and W. P. Rowe, Virology, in press. 13 A clone of fibroblasts (C13), derived from the BHK-21 line,' was obtained from Professor M. Stoker, Giasgow, Scotland, and was used at the 80th-lOOth generations since cloning. 14 Pope, J. H., and W. P. Rowe, J. Exptl. Med., 120, 121 (1964). 16 Black, P. H., W. P. Rowe, H. C. Turner, and R. J. Huebner, these PROCEEDINGS, 50, 1148 (1963). 16 Defendi, V., J. Lehman, and P. Kraemer, Virology, 19, 592 (1963). 17 Black, P. H., and W. P. Rowe, Proc. Soc. Exptl. Biol. Med., 114, 721 (1963). 18 Gotlieb-Stematsky, T., and R. Shilo, Virology, 22, 314 (1964). 19 Dulbecco, R., personal communication. 20 Le Bouvier, G., personal communication. 21 Crawford, L. V., and P. H. Black, Virology, 24, 388 (1964). 22 Mayor, H. D., R. M. Jamison, and L. E. Jordan, Virology, 19, 359 (1963). 23Stoker, M., and P. Abel, in Cold Spring Harbor Symposia on Quantitative Biology, vol. 17, (1962), p. 375. 24 Black, P. H., unpublished data. 25 Vinograd, J., R. Bruner, R. Kent, and J. Weigle, these PROCEEDINGS, 49, 902 (1963).

Total social isolation in monkeys

Abstract: Human social isolation is recognized as a problem of vast importance. Its effects are deleterious to personal adjustment, normal heterosexual development, and control of aggressive and delinquent behaviors. Isolation generally arises from breakdowns in family structures resulting 'in orphaned or semiorphaned .children or in illegitimate children who, for one reason or another, are raised in institutions, inadequate foster homes, or, occasionally, in abnormal homes with relatives.

Localization of dna complementary to ribosomal rna in the nucleolus organizer region of drosophila melanogaster.

Abstract: * The work reported has been done under USPHS grant GM 9912. t Career Scientist, Health Research Council of the City of New York. 1 Hungerford, D., J. Morphol., 97, 497 (1955). 2Beatty, R. A., Chromosoma, 8, 585 (1957). Levan, A., T. C. Hsu, and H. F. Stich, Hereditas, 48, 677 (1962). 4Ford, E. H. R., and D. H. M. Woollam, Exptl. Cell Res., 32, 320 (1963). 6 Crippa, M., Chromosoma, 15, 301 (1964). 6 Stich, H. F., and T. C. Hsu, Exptl. Cell Res., 20, 248 (1960). 7Hsu, T. C., Intern. Rev. Cytol., 12, 69 (1961). 8 Russell, L. B., Progr. Med. Genet., 2, 230 (1962). 9 Painter, T. S., Genetics, 12, 379 (1927). 10 Carter, T. C., M. F. Lyon, and R. J. S. Phillips, J. Genet., 53, 154 (1955). 11 Ford, C. E., J. L. Hamerton, D. W. H. Barnes, and J. F. Loutit, Nature, 177, 452 (1956). 12 Russell, L. B., and J. W. Bangham, Genetics, 46, 509 (1961). 13 Ohno, S., and B. M. Cattanach, Cytogenetics, 1, 129 (1962). 14 Dunn, L. C., D. Bennett, and A. B. Beasley, Genetics, 47, 285 (1962). 15 Geyer-Duszynska, I., ChroMwsoma, 15, 478 (1964). 16 Smith, L. S., J. Exptl. Zool., 132, 51 (1956). 17Ferguson-Smith, M. A., Cytogenetics, 3, 124 (1964). 18 Ford, E. H. R., and D. H. M. Woollam, Stain Technol., 38, 271 (1963). 19 Ohno, S., and T. S. Hauschka, Cancer Res., 20, 541 (1960).

Phosphorylation of nucleic acid by an enzyme from T4 bacteriophage-infected Escherichia coli

Abstract: 'I Martin, R. G., and B. N. Ames, J. Biol. Chem., 236, 1372 (1961). 15 For references to individual enzymes, see Snell, E. E., in The Mechanism of Action of Water Soluble Vitamins, Ciba Foundation Study Group No. 11, ed. A. V. E8. de Reuck and A. O'Connor (London: Churchill, 1961), pp. 18-37. 16 Under the same conditions PLP was observed to interact with serum albumin with appearance of absorption maxima at 332 and 415 m/A, as described by W. B. Dempsey and H. N. Christensen [J. Biol. Chem., 237, 1113 (1962)]. 17 The activating effects of PLP and Fe+++ on these earlier preparations9 remain unexplained but were partially due to stabilizing effects on the enzyme under the assay conditions then in use. They could be duplicated by Tweens, and hence provide no evidence for a role of PLP in action of the enzyme. Neither crude nor pure preparations of enzyme prepared and assayed by the present procedure show these effects. 18 Rabinowitz, J. C., and E. E. Snell, J. Biol. Chem., 176, 1157 (1948). 19 Shore, P. A., A. Burkhalter, and V. H. Cohn, Jr., J. Pharm. Exptl. Therap., 127, 182 (1959). 20 Du Vigneaud, V., and 0. K. Behrens, J. Biol. Chem., 117, 27 (1937). 21 Wallach, O., Ber., 15, 644 (1882).

The twisted circular form of polyoma viral DNA.

Abstract: The major part of the DNA from polyoma virus has been shown to consist of circular base-paired duplex molecules without chain ends1–3 The intertwined circular form accounts for the ease of renaturation4 of this DNA and the failure of the strands to separate in strand-separating solvents1–3

On the evolution of the genetic code

Abstract: The origin of the genetic code is not merely an evolutionary juggling of codon assignments until some optimal configuration is achieved. I t is, rather, the more interesting and profound problem of how codon assignments arose. This is part and parcel of the origin of a translating mechanism. A plausible scheme for the evolution of translation starting from a simple class of nucleic acid components is presented. Such an evolution may appear unique, idiosyncratic, when viewed only in terms of structural details. However, in its general features, on a more fundamental level, this evolution is a prototype study in the refinement of a process, in the emergence of macro-order. In approaching the evolution of the genetic code the biologist will be forced to reexamine many of his fundamental prejudices, indeed, the meaning of Biology itself.

Commutators of singular integral operators.

Abstract: where x, y are points in n-dimensional Euclidean space R" and k(x) is a homogeneous function of degree -n with mean value zero on xl = 1, and let B(f) = b(x)f(x). It is well known (see ref. 1) that if k anid b are sufficiently smooth and b is bounded, then (AB BA)(0/0ax) and (0/ax) (AB BA) are bounded operators in Lp, I

Spin-labeled biomolecules.

Abstract: are remarkably stable and inert,1 and show sharp, well-resolved, and simple paramagnetic resonance spectra2 that are sensitive to molecular motion,3 and, to a lesser extent, sensitive to polarity of the molecular environment.4 As shown below, such nitroxide radicals containing an isocyanate group can be bound to proteins and synthetic polypeptides in a manner similar to that used previously to attach fluorescent dyes.5 Here we report a preliminary study of the paramagnetic resoiiance of a nitroxide radical bonded to bovine serum albumin and to poly-L-lysine. It is evident from the present study that there are many other potential applicatioiis of this method to biological systems. Materials and Methods.-Preparation of 2, 2, 6, 5-tetramethyl-3-isocyanatopyrrolidine-1-oxyl (II): 2, 2, 5, 5-Tetramethyl-3-aminopyrrolidone-1-oxyl (III) was synthesized from triacetonamine by the method of Rosantzev and Krivitzkaya.6 NCO NH2

Cytoplasmic inheritance of the organization of the cell cortex in paramecium aurelia

Abstract: Y1,Y2,. . . be a sequence of independent two-valued random variables, Yn+i = -s or f3 + ns with probabilities (1 W) and W, where s is a small positive number and W is then determined by the condition -E(Y.) = aV(Yn). Verify that the probability that for some n, 3 + Y, + . . . + Yn > 0 converges to 1/(1 + ad) as s -. 0, and let X,, = Yn E(Yn). This completes the proof. The theorem can be extended to say that for each y > 0, if rT is the least n if any for which (Xi + . . . + Xn) . -yT +GI + . . . + An) + .(V. + * * * + Vn). then the probability that there is some n < rz for which (1) holds is less than (,y/(( + 3))(1/(1 + ac)); and this bound is sharp. The material of this note, including proofs of Lemmas 1 and 2, will appear as part of our forthcoming book, How to Gamble If You Must (New York: McGrawHill), Theorems 2.12.1 and 9.4.1, and an illustrative application of the theorem will appear in the forthcoming article, \"A sharper form of the Borel-Cantelli lemma and the strong law\" by L. E. Dubins and D. A. Freedman.

Studies on the role of protein synthesis in the regulation of corticosterone production by adrenocorticotropic hormone in vivo

Abstract: ** Recipient of a Career Scientist Award of the Health Research Council of the City of New York under contract no. 1-336. 1 Marks, P. A., E. R. Burka, and D. Schlessinger, these PROCEEDINGS, 48, 2163 (1962). 2Warner, J. R., P. M. Knopf, and A. Rich, these PROCEEDINGS, 49, 122 (1963). 3 Gierer, A., J. Mol. Biol., 6, 148 (1963). 4 Mathias, A. P., R. Williamson, H. E. Huxley, and S. Page, J. Mol. Biol., 9, 154 (1964). 5 Wettstein, F. O., T. Staehelin, and H. Noll, Nature, 197, 430 (1963). 6Penman, S., K. Scherrer, Y. Becker, and J. E. Darnell, these PROCEEDINGS, 49, 654 (1963). 7Korner, A., and A. J. Munro, Biochem. Biophys. Res. Commun., 11, 235 (1963). 8Clark, M. F., R. E. F. Matthews, and R. K. Ralph, Biochem. Biophys. Res. Commun., 13, 505 (1963). 9 Gilbert, W., J. Mol. Biol., 6, 374 (1963). 10 Schlessinger, D., J. Mol. Biol., 7, 569 (1963). 11 Rifkind, R. A., L. Luzatto, and P. A. Marks, these PROCEEDINGS, 52, 1227 (1964). 12 Warner, J. R., A. Rich, and C. E. Hall, Science, 138, 1309 (1962). 13 Slayter, H. S., J. R. Warner, A. Rich, and C. E. Hall, J. Mol. Biol., 7, 652 (1963). 14 Monroy, A., and A. Tyler, Arch. Biochem. Biophys., 103, 431 (1963). 15 Hultin, T., Develop. Biol., 10, 305 (1964). 16 Marks, P. A., R. A. Rifkind, and D. Danon, these PROCEEDINGS, 56, 336 (1963). 17 Rifkind, R. A., D. Danon, and P. A. Marks, J. Cell Biol., 22, 599 (1964). 18 Glowacki, E. R., and R. L. Millette, J. Mol. Biol., 11, 116 (1965). '9 Marks, P. A., E. R. Burka, R. A. Rifkind, and D. Danon, in Synthesis and Structure of Macromolecules, Cold Spring Harbor Symposia on Quantitative Biology, vol. 22 (1963), p. 599. 20Borsook, H., C. L. Deasy, A. J. Haagen-Smit, G. Keighley, and P. H. Lowy, J. Biol. Chem., 196, 699 (1952). 21 Szeinberg, A., and P. A. Marks, J. Clin. Invest., 40, 914 (1961). 22 Kornberg, A., in Methods in Enzymology (New York: Academic Press, 1955), vol. 2, p. 497. 23Lohrmann, K., and 0. Meyerhoff, Biochem. Z., 273, 60 (1934). 24 Goodman, H., and A. Rich, Nature, 199, 318 (1963). 25 Hardesty, B., J. J. Hutton, R. Arlinghaus, and R. Schweet, these PROCEEDINGS, 50, 1078 (1963). 26Burka, E. R., and P. A. Marks, Nature, 204, 659 (1964). 27 Gross, P., J. Exptl. Zool., 157, 21 (1964). 28 Maggio, R., A. NIonroy, A. M. Rinaldi, and Al. L. Vittorelli, Compt. Rend., 260, 1293 (1965). 29 Spirin, A. S., and M. Nemer, in preparation.

Regulation of hibernating periods by temperature.

Abstract: * Supported by grants G 24052 and GE 3612 from the National Science Foundation. 1 Beauchesne, G., M. Leboeuf, and R. Goutarel, in Regulateurs Naturels de la Croissance Vegtale (Paris: Centre National de la Recherche Scientifique, 1964), p. 119. 2 Letham, D. A., in Regulateurs Naturels de la Croissance Vegetale (Paris: Centre National de la Recherche Scientifique, 1964), p. 109; and ref. 6 (below). 3Miller, C. O., these PROCEEDINGS, 47, 170 (1961); and refs. 13 and 16 (below). 4Letham, D. S., and C. 0. Miller, Plant Cell Physiol., in press. 6 Letham, D. S., J. S. Shannon, and I. R. McDonald, Proc. Chem. Soc., 1964, 230. 6 Letham, D. S., Life Sci., 2, 569 (1963). 7 Kefford, K. P., Science, 142, 1495 (1963). 8 Miller, C. O., in Modern Methods of Plant Analysis (Berlin: Springer-Verlag, 1963), vol. 6, p. 194. 9 McCalla, D. R., D. J. Moore, and D. Osborne, Biochim. Biophys. Acta, 55, 522 (1962). 10 Hurlbert, R. B., H. Schmitz, A. F. Brumm, and V. R. Potter, J. Biol. Chem., 209, 23 (1954). 11 Jacobson, K. B., Science, 138, 515 (1962). 12 Khym, J. X., and W. E. Cohn, J. Am. Chem. Soc., 76, 1818 (1954). 13 Miller, C. O., Plant Physiol., 37, xxxv (1962). 14 Loeffier, J. E., and J. Van Overbeek, in Regulateurs Naturels de la Croissance V~ggtale (Paris: Centre National de la Recherche Scientifique, 1964), p. 77. 15 Fox, J. E., Plant Physiol., 39, xxxi (1964). 16 Miller, C. O., and F. H. Witham, in Rlgulateurs Naturels de la Croissance V~ggtale (Paris: Centre National de la Recherche Scientifique, 1964), p. I (erratum).

Evidence for the natural occurrence of zeatin and derivatives: compounds from maize which promote cell division.

Abstract: Three laboratories previously have obtained from Zea mays kernels (milk stage) one or more 6-(substituted)aminopurines capable of greatly promoting cell division in plant tissue cultures.1-3 At least two of the laboratories have worked on a single compound4 which has been identified as 6-(4-hydroxy-3-methylbut-2-enyl)aminopurine.5 The name zeatin has been applied to this particular compound.6 Only a small portion of the total cell-division activity in crude extracts from kernels seems to be due to zeatin'-3 and its actual existence in the kernel has been questioned.7 We now present evidence strongly indicating that zeatin does occur naturally in its unsubstituted form and also in nucleoside and nucleotide forms. Assay.-The active materials in the maize extracts were detected by using the soybean (Glycine max, var. Acme) tissue test.3' 8 This tissue requires a substance like zeatin for continued cell division and has proved to be very sensitive to zeatin and similar compounds. For example, in recent tests we have obtained measurable growth responses to as little as 5 X 10-11 M zeatin. Most assays were performed with small quantities of extracts which contained rather low concentrations of active materials. With such low concentrations, the soybean test shows considerable variation of fresh weights for individual pieces in a particular assay but still a high degree of reproducibility from test to test. Repeats of all experiments reported here have given consistent results. Stock cultures of the soybean tissue have been maintained on a medium containing (mg/liter): KH2PO4, 300; KNO3, 1000; NH4NO3, 1000; Ca(NO3)2 .4H20, 500; MgSO4-7H20, 71.5; KCl, 65; MnSO4 .4H20, 14; NaFe ethylenediaminetetraacetate, 13.2; ZnSO4 7H20, 3.8; H3BO3, 1.6; Cu(NO3)2.3H20, 0.35; (NH4)6 Mo7024 *4H20, 0.1; i-inositol, 100; nicotinic acid, 0.5; pyridoxine HCI, 0.1; thiamin * HCl, 0.1; a-naphthaleneacetic acid, 2; kinetin, 0.5; sucrose, 30,000; and Bacto-agar, 10,000. The pH was adjusted to 5.8 (NaOH). A preparation to be tested for cell-division activity was added to this medium with the kinetin omitted, the pH was adjusted to 5.8 with NaOH or HCl, and sterilization was achieved by autoclaving. Each of four 125-ml Erlenmeyer flasks containing 50 ml of hardened medium was planted with four pieces of the stock soybean tissue. After growth for 28 days at 27°C and constant fluorescent lighting at about 40 ft-c, the pieces were weighed individually. The fresh weight averages indicate relative amounts of cell division. Extracts.-Frozen kernels (milk stage) of Zea mays, var. Golden Cross Bantam, were extracted by macerating in either cold or boiling 95 per cent ethanol. The final concentration of ethanol was adjusted to 70 per cent (assuming the weight of kernel was due entirely to water). The extract was cooled and the filtered precipitate discarded. The filtrate was used in all of the experiments. Chromatography.-Ethanol solutions or other preparations were streaked on sheets of Whatman #1 filter paper. For development, one of the following mix-

The enzymatic cleavage of beta-carotene into vitamin A by soluble enzymes of rat liver and intestine

Abstract: That 13-carotene can serve as a precursor of vitamin A in mammals was demonstrated almost 40 years ago." 2 In spite of innumerable nutritional and chemical studies on this reaction, however, neither the pathway nor the mechanism of vitamin A formation has been clarified.3-5 With respect to the pathway of vitamin A formation, two major hypotheses have been suggested: (1) carotene is cleaved at the central 15-15' double bond to yield two molecules of vitamin A, and (2) carotene is cleaved peripherally to yield one molecule of vitamin A via a series of 13-apo-carotenals.4 Although f3-apo-carotenals have been found in nature,6 are highly effective biologically, and are converted to vitamin A in the mammal,4 they do not accumulate during the cleavage of ,8-carotene in vivo.7 The cleavage of ,8-carotene to vitamin A seemingly proceeds by an oxidative reaction. In isolated sections of intestine oxygen is required for the conversion of carotene to vitamin A,8 a requirement which correlates better with the cleavage reaction than with the absorption of carotene into gut slices.9 Furthermore, oxygen'8 is incorporated into vitamin A in the liver of carotene-treated animals when 0218 gas is used but not when H2018 is employed.'0 Purely chemical studies also accord with an oxidative cleavage mechanism."' 12 Although the intestine seems to be the major organ in the rat for carotene cleavage into vitamin A,7 1" the liver also catalyzes this reaction.'4 Interestingly, bile salts are necessary for the uptake and cleavage of carotene by gut slices,7 but are not required for cleavage in the liver.'4 In the present report an enzyme has been found in the supernatant solution of rat liver and intestine which converts 13-carotene into retinal and retinol as its sole products. Oxygen is required for the reaction, and the immediate product is retinal. The enzyme is inhibited by sulfhydryl binding reagents and by ferrous-ion chelating agents. The enzyme has been tentatively designated as 1-carotene 15-15' oxygenase. Materials and Methods.-Preparation of radioactive #-carotene: Sodium acetate J-C'4 was added to growing cultures of Phycomyces blakesleeanus, and the synthesized ,B-carotene was extracted and purified as previously described.'5 16 The three times recrystallized compound was greater than 98% pure, as judged by two-dimensional chromatography on silica gel thin-layer plates, and had a specific activity of 6560 cpm per Mg. The labeled ,B-carotene was stored in hexane in the presence of a-tocopherol in a red glass container in the cold. Just prior to each experiment a suitable quantity was purified through a small column of 6% water-deactivated alumina, dried in the dark under nitrogen, dissolved in 0.05 ml of 20% Tween 40 in distilled acetone, and made up to a suitable volume with 0.15 M tris-hydroxymethyl-aminomethane (Tris) buffer, pH 8.0. Preparation of organ homogenates: Male or female rats of the Wistar strain weighing 150-300 gm were anesthetized with ether, opened by midline incision, and the liver or kidneys were quickly removed and washed in saline. The upper half of the intestine was also removed, cut longitudinally to expose the mucosal surface, and washed in cold saline. Each tissue was minced on a cold Petri plate and homogenized with a loose-fitting, motor-driven glass homogenizer in 5 vol of cold 0.15

Evidence for virus-specific noncapsid proteins in poliovirus-infected HeLa cells.

Abstract: tone fractions III and IV in cells in which DNA is not undergoing replication, appears to be a general characteristic of higher organisms, plants, and animals. It further appears that the inhibition of DNA synthesis in cells in which such synthesis is occurring promptly stops the formation of histones of groups I and II. It is these histones which have been shown to be the most effective in inhibition of DNA-dependent RNA synthesis in reconstituted nucleohistones.11 The tentative conclusion may be drawn that any portion of the genome which is associated with histones I and II is not available for transcription without replication of DNA. Summary. -The use of an ion-exchange chromatographic technique for the fractionation of histories has showve that only two classes of histones turn over in cells in which DNA is not undergoing replication. These are histories of groups III and IV, and, in addition, the proteins of the so-called runoff peak which precedes the elution of the histones proper. The lysine-rich histones I and II on the contrary are only formed in cells in which DNA is undergoing replication.

RNA codewords and protein synthesis, VII. On the general nature of the RNA code.

Abstract: In this report, the template activities of twenty-six additional trinucleotides are described and related to the nature of the RNA code. This builds on earlier work of Nirenberg and others, which describes the template activities of nineteen additional trinucleotides and nucleotide sequences suggested for RNA codons corresponding to amino acids. While still far from an "invariant dictionary" at this stage in the research, a table of possible nucleotide sequences is provided.

Contact inhibition, macromolecular synthesis, and polyribosomes in cultured human diploid fibroblasts

Abstract: The contact inhibition of locomnotion in human cells has been described by Abercrombie.i When normal diploid fibroblasts growing on a glass surface come inito contact, an adhesion forms and cell movement in that direction stops. As the resulting "monolayer" of diploid cells becomes confluent, their growth rate also decreases markedly., 2 In consequence, an upper limit is set for the population density of a given diploid cell culture which is not determined by properties of the nedium. Human cell lines in which contact inhibition of growth is not operative (in general, heteroploid cells) form multilayered sheets in stationary culture, and attain population densities up to ten times those of human diploid cells. The present communication describes some of the molecular events associated with the decreasing growth rate of cultured human diploid cells as they become confluent. The possible causal role of cellular contact is also considered.