Showing papers by "University of Perugia published in 1991"

Structure and origin of the acute promyelocytic leukemia myl/RAR alpha cDNA and characterization of its retinoid-binding and transactivation properties.

Abstract: Acute promyelocytic leukemia (APL) is characterized by the 15;17 chromosomal translocation Cloning experiments have established that the chromosome 17 breakpoint maps to the RAR alpha and the 15 to the myl locus The resulting chimeric gene is transcribed as a myl/RAR alpha fusion mRNA By isolating both normal myl and APL myl/RAR alpha cDNAs, we showed that the myl/RAR alpha mRNA encodes for a putative fusion protein with a molecular weight of about 103 kDa, which is made up of 530 amino acids derived from the myl N-terminus and 402 amino acids originating from the RAR alpha C-terminus The protein includes the RAR alpha DNA and retinoid-binding regions but lacks the A portion of the N-terminal region (A/B region) which is thought to contain one of the RAR alpha transactivation domains The myl/RAR alpha protein acted as a retinoid-inducible transcription factor with both ligand-independent repressor and ligand-dependent activator functions in transactivation experiments of a retinoic acid-responsive gene Myl/RAR alpha exerted this dual function three times more effectively than RAR alpha and had about 10-fold greater affinity for RA than RAR alpha Comparison of myl/RAR alpha genomic and cDNA sequences from the same case demonstrated that both chromosome 15 and 17 breakpoints occurred within introns and the myl and RAR alpha sequences are spliced in the same polyadenylated RNA

Translocation breakpoint of acute promyelocytic leukemia lies within the retinoic acid receptor alpha locus.

Abstract: Acute promyelocytic leukemias (APLs) are characterized by a reciprocal balanced translocation that involves chromosomes 15 and 17 [t(15;17)]. We report the isolation and characterization of one of the two reciprocal break sites and demonstrate that the chromosome 17 breakpoint lies within the retinoic acid receptor alpha locus. Nucleotide sequencing of the 15;17 cross-over junction on 15q+ showed that the retinoic acid receptor alpha gene is truncated within its first intron, 370 base pairs upstream from the splicing donor site of exon II. Such a recombination would be expected to generate abnormal RAR alpha mRNA and protein. Southern blot analysis of a number of APLs with chromosome 15- and 17-derived DNA probes revealed similar 15;17 recombinations in the majority of other APLs. Our data are strong evidence that the retinoic acid receptor alpha gene plays a crucial role in the leukemogenesis of APL.

Th1 and Th2 cytokine secretion patterns in murine candidiasis: association of Th1 responses with acquired resistance.

Abstract: Two chemically mutagenized agerminative variants of Candida albicans were used to immunize mice against challenge with highly virulent cells of the parent strain. Although both mutants (Vir- 3 and Vir- 13) resulted in nonlethal infection and could be recovered from mouse organs for many days after the intravenous inoculation of 10(7) to 10(6) cells, significant protection to systemic challenge with virulent C. albicans was induced by only one (Vir- 3) of the two variants. Anticandidal resistance in Vir- 3-infected mice was associated with the occurrence in vivo of strong delayed-type hypersensitivity to Candida antigen, detection in vitro of highly fungicidal effector macrophages, and presence in the serum of a large proportion of Candida-reactive antibodies of the immunoglobulin G2a isotype. Bulk cultures of purified CD4+ lymphocytes from mice infected with either mutant were compared for their ability to produce gamma interferon (IFN-gamma), interleukin-2 (IL-2), IL-4, and IL-6 in vitro. After stimulation with specific antigen, CD4+ cells from Vir- 3-immunized mice released large amounts of the Th1-specific cytokines, IFN-gamma and IL-2, at a time when CD4+ cells from Vir- 13-infected mice predominantly secreted the characteristic Th2 cytokines, IL-4 and IL-6. These results were confirmed by quantitative analysis of cytokine-producing Th1 and Th2 cells. In addition, only mice infected with Vir- 3 displayed a high frequency of CD8+ cells with the potential for in vitro lysis of yeast-primed bone marrow macrophages. Purified CD4+ cells from Vir- 3-infected mice, but not a mixture of these cells with CD4+ lymphocytes from mice infected with Vir- 13, could adoptively transfer delayed-type hypersensitivity reactivity onto naive mice. Taken together, these data suggest that both Th1 and Th2 CD4+ lymphocytes may be activated during experimental C. albicans infection in mice.

Active polysomes in the axoplasm of the squid giant axon.

Abstract: Axons and axon terminals are widely believed to lack the capacity to synthesize proteins, relying instead on the delivery of proteins made in the perikaryon. In agreement with this view, axoplasmic proteins synthesized by the isolated giant axon of the squid are believed to derive entirely from periaxonal glial cells. However, squid axoplusm is known to contain the requisite components of an extra-mitocliondrial protein synthetic system, including protdn factors, tRNAs, rRNAs, and a heterogeneous family of mRNAs. Hence, the giant axon could, in principle, maintain an endogenous protein synthetic capacity. Here, we report that the squid giant axon also contains active polysomes and niRNA, which hybridizes to a riboprobe encoding murine neurofilament protein. Taken together, these findings provide direct evidence that proteins (including the putative neuron-specific neurofilament protein) are also synthesized de novo in the axonal compartment.

Identification and characterization of novel human endogenous retroviral sequences prefentially expressed in undifferentiated embryonal carcinoma cells

Abstract: A novel endogenous retroviral sequence (ERV-9) has been isolated from a human embryonal carcinoma cDNA library by hybridization to a probe containing a recently described human repetitive element. DNA sequence analysis of the 4kb cDNA insert (pHE.1) revealed the presence of ORFs potentially coding for putative retrovirus-related gag, pol and env proteins. Northern blot and RNase protection experiments showed that RNA homologous to the pHE.1 insert is detected only in embryonal carcinoma cells as a 8 kb mRNA, and its expression is negatively regulated during retinoic acid induced differentiation of the human teratocarcinoma cell line NT2/D1. Using a pol specific probe we have isolated a genomic locus containing the ERV-9 sequences. Characterization by restriction enzyme analysis and DNA sequencing allowed us to define LTR-like sequences, that are composed by a complex array of subrepetitive elements. In addition we show that ERV-9 LTR sequences are capable to drive expression of linked CAT gene in a cell specific manner as LTR promoter activity has been detected only in NT2/D1 cells.

ACE-inhibition increases hepatic and extrahepatic sensitivity to insulin in patients with Type 2 (non-insulin-dependent) diabetes mellitus and arterial hypertension

Abstract: To assess the effects of ACE-inhibition on insulin action in Type 2 (non-insulin-dependent) diabetes mellitus associated with essential hypertension, 12 patients with Type 2 diabetes (on diet and oral hypoglycaemic agents) and arterial hypertension were examined on two occasions, in a single blind, cross-over study after two days of treatment with either captopril or a placebo. The study consisted of a euglycaemic-hyperinsulinaemic clamp (two sequential steps of insulin infusion at the rates of 0.25 mU.kg-1.min-1 and 1 mU.kg-1.min-1, 2 h each step), combined with an infusion of 3-3H-glucose to measure the rate of hepatic glucose production and that of peripheral glucose utilization. The results show that blood pressure was lower after captopril (sitting, systolic 148 +/- 5 mm Hg, diastolic 89 +/- 2 mm Hg) compared to placebo (155 +/- 6 and 94 +/- 2 mm Hg) (p less than 0.05). Captopril treatment resulted in a more suppressed hepatic glucose production (2.7 +/- 0.4 vs 4.94 +/- 0.55 mumol.kg-1.min-1), and a lower plasma non-esterified fatty acid concentration (0.143 +/- 0.05 vs 0.200 +/- 0.05 mmol/l) (captopril vs placebo, p less than 0.05) at the end of the first step of insulin infusion (estimated portal plasma insulin concentration 305 +/- 28 pmol/l); and in a greater glucose utilization (36.5 +/- 5.1 vs 28 +/- 3.6 mumol.kg-1.min-1, p less than 0.001) at the end of the second step of insulin infusion (arterial plasma insulin concentration of 604 +/- 33 pmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of quinolinic and kynurenic acid content in the rat brain: effects of endotoxins and nicotinylalanine.

Abstract: Quinolinic acid, an endogenous excitotoxin, and kynurenic acid, an antagonist of excitatory amino acid receptors, are believed to be synthesized from tryptophan after the opening of the indole ring. They were measured in the rat brain and other organs using gas chromatography-mass spectrometry or HPLC. The enzyme indoleamine 2,3-diox-ygenase, capable of cleaving the indole ring of tryptophan, was induced by administering bacterial endotoxins to rats, which significantly increased the brain content of both quinolinic and kynurenic acids. Nicotinylalanine, an analogue of kynurenine, inhibited this endotoxin-induced accumulation of quinolinic acid while potentiating the accumulation of-kynurenic acid. The possibility of significantly increasing brain concentrations of kynurenic acid without a concomitant increase in quinolinic acid may provide a useful approach for studying the role of these electrophysiologically active tryptophan metabolites in brain function and preventing the possible toxic actions of abnormal synthesis of quinolinic acid.

Predictive factors of delayed emesis in cisplatin-treated patients and antiemetic activity and tolerability of metoclopramide or dexamethasone. A randomized single-blind study.

Abstract: To prevent delayed emesis induced by cisplatin (mean dose 90 mg/m2), 120 consecutive patients were randomized to receive, in a 7-day crossover design, oral metoclopramide (20 mg q.i.d.), dexamethasone (1 mg q.i.d.) or placebo (two tablets q.i.d.) starting 24 hours after the end of chemotherapy. Complete protection from nausea, but not from vomiting. was significantly increased by both dexamethasone and metoclopramide with respect to placebo. Important prognostic factors favoring the appearance of delayed emesis were incomplete protection from vomiting during the first 24 hours after cisplatin, female gender, and highest cisplatin doses. Tolerability of both drugs was good. Larger and randomized controlled trials are necessary to identify better preventive treatment of delayed emesis induced by cisplatin.

The influence of air temperature on the starting dates of the pollen season of alnus and populus

Abstract: In this work we have studied the influence of air temperature on the starting dates of Alnus and Populus pollination in two different climatic regions in Europe: central Italy and The Netherlands. The start of the Alnus pollen season varied between 27th January and 16th February in the Italian stations while in The Netherlands it showed an average delay of about one month. For Populus the beginning of the pollen season was delayed on an average 15 days at Dutch places compared to central Italy. In the former it varied between 14th March and 21st April while in the latter between 28th February and 24th March. Significant correlations exist between the beginning of pollination for these taxa and temperature conditions in the preceding periods. The highest correlations found were with daily mean decade temperature for three decades before the average starting dates of the pollen season. These correlations were better for The Netherlands than for central Italy perhaps because the temperature in Holla...

Immunohistochemical detection of the multidrug transport protein P170 in human normal tissues and malignant lymphomas.

Abstract: Two monoclonal antibodies, MRK16 and C219, both directed at the 170 kDa P-glycoprotein multidrug resistance agent, were applied to frozen sections or cytospin preparations from normal human tissues and 60 non-Hodgkin's malignant lymphomas. Adrenal gland, kidney, liver and pancreas were always stained by the reagents, albeit with slightly different patterns. Brain capillaries as well as macrophages and some elements of the bone marrow, peripheral blood, ovarian stroma and colonic, gastric and jejunal mucosa were positive in all examined preparations. There were differences in the staining patterns with the two antibodies. Among the 60 non-Hodgkin's lymphomas, 25 contained a number of positive cells, which ranged from 2% to 100%. No correlation was seen between the expression of P170 and histological type, stage, clinical symptoms or growth fraction. A close relationship was shown between the presence of P170 positive elements and the clinical course of the disease (P less than 0.001).

y-scaling analysis of quasielastic electron scattering and nucleon momentum distributions in few-body systems, complex nuclei, and nuclear matter.

Abstract: The approach to y scaling previously adopted to obtain the nucleon momentum distribution in the two- and three-nucleon systems is extended to the case of complex nuclei and nuclear matter. The basic elements of this approach, which takes properly into account nucleon binding and momentum, are reviewed. A new method of analysis, which allows one to obtain the experimental asymptotic scaling function from inclusive cross sections even if these data are affected by final-state interactions, is proposed and illustrated. By such a method, the asymptotic scaling functions of $^{3}\mathrm{He}$, $^{4}\mathrm{He}$, $^{12}\mathrm{C}$, $^{56}\mathrm{Fe}$, and nuclear matter are obtained from recent experimental data and it is demonstrated that, particularly at high negative values of the scaling variable, the available data points at the highest value of the momentum transfer are affected by final-state interaction and cannot therefore be considered to represent the asymptotic scaling function. It is shown that, unlike what is commonly stated, the nucleon momentum distribution is not simply defined in terms of the derivative of the asymptotic scaling function, but as a sum of such a derivative plus the derivative of a quantity, the binding correction, generated by the removal energy distribution of nucleons embedded in the nuclear medium.The binding correction and its derivative are evaluated with various types of spectral functions, and the nucleon momentum distributions in $^{3}\mathrm{He}$, $^{4}\mathrm{He}$, $^{12}\mathrm{C}$, $^{56}\mathrm{Fe}$, and nuclear matter are obtained up to nucleon momenta k\ensuremath{\approxeq}500 MeV/c. For few-body systems the obtained momentum distributions satisfactorily agree with the ones extracted from (e,e'p) reactions and with theoretical calculations performed within Faddeev or variational approaches, whereas for complex nuclei they qualitatively agree with predictions of theoretical many-body approaches which take nucleon-nucleon correlations into account and, at the same time, at k\ensuremath{\ge}350 MeV/c they are larger by orders of magnitude than the ones predicted by mean field approaches. Such a result does represent unambiguous evidence of correlation effects in nuclei.

Inhibition of human breast cancer cell (MCF-7) growth in vitro by the somatostatin analog SMS 201-995: effects on cell cycle parameters and apoptotic cell death.

Abstract: Somatostatin (SS) and SS analogs have been shown to exert an antiproliferative effect on several transplantable tumors in animals and to reduce the growth of pancreatic, pituitary, and mammary tumor cells in vitro. We evaluated the effects that the SS analog SMS 201-995 exerts on growth, cell-cycle parameters, and suicidal cell death (apoptosis) of human breast cancer cells (MCF-7) in vitro. SMS 201-995 significantly reduced the MCF-7 cell growth induced by serum, estradiol, insulin, and insulin-like growth Factor-I in both short term and long term experiments. The effect was maximal when 10 nM estradiol was used as mitogen in long term cultures. SMS 201-995 treatment produced a slight but transient accumulation of cells in the G2/M phase but did not cause any noteworthy reduction in the percentage of proliferating cells. There was, instead, a time-related increase in the number of cells with the flow-cytometric characteristics of apoptosis in the cultures treated with the SS analog, which correlated well with its growth-inhibiting activity. It would, therefore, seem that SMS 201-995 exerts its inhibitory effect on MCF-7 cell growth in vitro mainly by enhancing the rate of programmed (or suicidal) cell death in the culture.

Macrophage colony-stimulating factor in murine candidiasis: serum and tissue levels during infection and protective effect of exogenous administration.

Abstract: Serum and tissue concentrations of the macrophage-specific colony-stimulating factor (CSF-1) and the number of CSF-1-responsive cells in bone marrow were investigated in mice chronically infected with a low-virulence strain of the opportunistic zoopathogenic yeast Candida albicans. CSF-1 levels in serum, brain, kidney, liver, and lung were significantly increased shortly after infection and remained elevated during the 2 weeks preceding the onset of specific T cell-dependent immunity. The number of monocytic precursor cells was also increased in the bone marrow of infected mice. When macrophages from naive donors were exposed in vitro to purified murine CSF-1, their anticandidal activity in vitro appeared to be enhanced. CSF-1 was also administered in vivo to prospective recipients of a lethal C. albicans challenge. The results showed that the factor could effectively potentiate the animals' resistance to the yeast, as shown by increased survival times and reduced recovery of viable C. albicans from the organs of the CSF-1-treated mice. Therefore, the present data suggest that CSF-1 is likely to contribute to early resistance to fungal infection and could be successfully exploited in experimental models of antifungal immunotherapy.

Genetic Variability and Biochemical Systematics of Domestic and Wild Cat Populations (Felis silvestris: Felidae)

Abstract: Genetic variability and phylogenetic relationships among domestic and wild populations of cats were studied by allozyme electrophoresis. Tissues were obtained from 67 specimens of European wild cats ( Felis silvestris silvestris ), African wild cats ( F. s. libyca ), and domestic cats from Italy; 54 presumptive loci were resolved. The average proportion of polymorphic loci and heterozygosity were P = 0.11, H = 0.042 in the wild cat, and P = 0.20, H = 0.066 in the domestic cat. Despite reduced genetic variability, local populations of wild cats were not inbred, as indicated by nonsignificant F IS values. Both F ST and Nei's genetic distances between domestic and wild populations were low ( F ST = 0.04; D = 0.0082). Dendrograms indicate that the domestic cat belongs to the African wild cat lineage, which supports current hypotheses on cat domestication. Based on the genetic evidence, we suggest that the European wild cat, the African wild cat, and the domestic cat belong to the same polytypic species ( Felis silvestris Schreber, 1777), and that the European and African wild cats diverged approximately 20,000 years ago.

The dawn phenomenon in type 1 (insulin-dependent) diabetes mellitus: magnitude, frequency, variability, and dependency on glucose counterregulation and insulin sensitivity.

Abstract: In 114 subjects with Type 1 (insulin-dependent) diabetes mellitus the nocturnal insulin requirements to maintain euglycaemia were assessed by means of i.v. insulin infusion by a Harvard pump. The insulin requirements decreased after midnight to a nadir of 0.102 +/- 0.03 mU.kg-1.min-1 at 02.40 hours. Thereafter, the insulin requirements increased to a peak of 0.135 +/- 0.06 mU.kg-1.min-1 at 06.40 hours (p less than 0.05). The dawn phenomenon (increase in insulin requirements by more than 20% after 02.40 hours lasting for at least 90 min) was present in 101 out of the 114 diabetic subjects, and its magnitude (% increase in insulin requirements between 05.00-07.00 hours vs that between 01.00-03.00 hours) was 19.4 +/- 0.54% and correlated inversely with the duration of diabetes (r = -0.72, p less than 0.001), but not with age. The nocturnal insulin requirements and the dawn phenomenon were highly reproducible on three separate nights. In addition, glycaemic control, state of counterregulation to hypoglycaemia and insulin sensitivity all influenced the magnitude of the dawn phenomenon as follows. In a subgroup of 84 subjects with Type 1 diabetes, the multiple correlation analysis showed that not only duration of diabetes (t = -9.76, p less than 0.0001), but also % HbA1 significantly influenced the magnitude of the dawn phenomenon (t = 2.03, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma profiles of adrenocorticotropic hormone, cortisol, growth hormone and prolactin in patients with untreated Parkinson's disease.

Abstract: Plasma profiles of prolactin, growth hormone, adrenocorticotropic hormone (ACTH) and cortisol were evaluated in a group of untreated patients with idiopathic Parkinson's disease and a group of healthy age-matched controls. Plasma integrated concentrations of all hormones except prolactin were significantly lower in the patients as compared with the controls; however, prolactin nocturnal peak concentration was significantly elevated in the patients; nocturnal growth hormone levels were significantly reduced in the Parkinson group; ACTH and cortisol plasma concentrations were also consistently lower during most of the day in the patients with Parkinson's disease. These data confirm the presence of a hypothalamic disturbance in patients with idopathic Parkinson's disease, which can affect pituitary function.

Changes in glial fibrillary acidic protein and karyotype during culturing of two cell lines established from human glioblastoma multiforme.

Abstract: Two human cell lines (GL15 and GL22) derived from glioblastoma multiforme were established and characterized by immunohistochemical and cytogenetic techniques. The expression of glial fibrillary acidic proteins and the karyotype were analyzed at different passages for both cell lines. The course of marker-pattern differed in the two cell lines. The main findings were a cell-density-dependent expression of glial fibrillary acidic protein in the cell line GL15 at all passages and a decreased expression of this protein over time in the cell line GL22. Both cell lines had hyperdiploid karyotypes and exhibited glioma-specific chromosomal abnormalities (gain of chromosome 7 and loss of chromosome 10). In the GL15 cell line no relevant chromosomal changes were produced during culturing, whereas in the GL22 cell line a hypodiploid clone appeared at the 42nd passage. The immunohistochemical and cytogenetic data resulting from this study confirm that the two cell lines established in our laboratory originated from astrocytic tumor cells.

Head and neck trauma in sporting activities. Review of 208 cases.

Abstract: Head and neck injuries due to sports and games represent 22.7% of all injuries admitted to the E.N.T. Department of the University of Perugia between 1980 and 1988. Epidemiological and causative factors of these injuries are examined by the authors, together with their treatment: the majority of accidents occurred during soccer games as a consequence of collisions between players. In these cases the most frequently recorded lesion was a nasal fracture. Other sporting activities were responsible for more serious injuries to the maxillo-facial bony, cartilaginous and soft tissue structures. Good results were achieved both on the anatomical and functional planes, except for a few cases of facial disruption and multiple mandibular fractures. The authors stress the importance of preventive measures, consisting of periodical medical check-ups, an adequate level of umpiring and the wearing of protective equipment, such as helmets and masks.

Activity of different 'killer' yeasts on strains of yeast species undesirable in the food industry.

Abstract: Killer strains of the genera Saccharomyces, Hansenula and Kluyveromyces were tested for killing activity against yeasts that cause trouble in the food inductry (in the genera Zygosaccharomyces, Kloeckera, Saccharomycodes and Schizosaccharomyces). Saccharomyces strains killed only Zygosaccharomyces rouxii strains, while non-Saccharomyces strains showed a wider anti-yeast spectrum. The Kluyveromyces phaffii killer strain was of particular interest because of its killer action against Kloeckera apiculata, Saccharomycodes ludwigii and Zygosaccharomyces rouxii.

Physical training and antiplatelet treatment in stage II peripheral arterial occlusive disease: alone or combined?

Abstract: The efficacy of physical training alone or combined with antiplatelet thera py (dipyridamole and aspirin) was studied in 30 patients with stage II peripheral arterial occlusive disease (PAOD).Patients were randomly allocated to one of the following groups: Group A— dipyridamole 75 mg three times daily and aspirin 330 mg once daily: Group B— physical exercise; Group C—physical exercise and dipyridamole 75 mg three time daily and aspirin 330 mg once daily.After six months' treatment the pain-free walking time (PFWT) and the max imum walking time (MWT) improved significantly (p < 0.05) in all three groups. In group A the PFWT lengthened by 35% (from 101.00 ± 34.56 to 137.32 ± 40.50 s) and the MWT by 38% (from 150.34 ± 55.60 to 207.26 ± 60.67 s); in group B the PFWT lengthened by 90% (from 90.65 ± 40.54 to 171.45 ± 55.60 s) and the MWT by 86% (from 145.39 ± 60.50 to 270.63 ± 63.61 s). When physical exer cise was associated with drugs as in group C, the PFWT lengthened by 120% (from 89.51 ± 43.89 to 196.72 ±51...

Wearable system for acquisition, processing and storage of the signal from amperometric glucose sensors.

Abstract: A wearable device for the acquisition, processing and storage of the signal from needle-type glucose sensors has been designed and developed as part of a project aimed at developing a portable artificial pancreas The device is essential to assess the operational characteristics of miniaturized sensors in vivo It can be connected to sensors operating at a constant potential of 065 Volts, and generating currents in the order of 10(-9) Amp It is screened and equipped with filters that permit data recording and processing even in the presence of electrical noise It can operate with sensors with different characteristics (1-200 nA full scale) The device has been designed to be worn by patients, so its weight and size have been kept to a minimum (250 g; 85 x 145 x 35 cm) It is powered by rechargeable Ni/Cd batteries allowing continuous operation for 72 h The electronics consists of an analog card with operational amplifiers, and a digital one with a microprocessor (Intel 80C196, MCS-96 class, with internal 16-bit CPU supporting programs written in either C or Assembler language), a 32 Kb EPROM, and an 8 Kb RAM where the data are stored The microprocessor can run either at 5 or 10 Mhz and features on-chip peripherals: an analog/digital (A/D) converter, a serial port (used to transfer data to a Personal Computer at the end of the 72 h), input-output (I/O) units at high-speed, and two timers The device is programmed and prepared to operate by means of a second hand-held unit equipped with an LCD display and a 16-key numeric pad(ABSTRACT TRUNCATED AT 250 WORDS)

Structure and chromosomal localization of DNA sequences related to ribosomal subrepeats in Vicia faba.

Abstract: Subrepeating sequences of 325 bp found in the ribosomal intergenic spacer (IGS) of Vicia faba and responsible for variations in the length of the polycistronic units for rRNA were isolated and used as probes for in situ hybridization. Hybridization occurs at many regions of the metaphase chromosomes besides those bearing rRNA genes, namely chromosome ends and all the heterochromatic regions revealed by enhanced fluorescence after quinacrine staining. The DNA homologous to the 325 bp repeats that does not reside in the IGS was isolated, cloned and sequenced. It is composed of tandemly arranged 336 bp elements, each comprising two highly related 168 bp sequences. This structure is very similar to that of the IGS repeats and ca. 75% nucleotide sequence identity can be observed between these and the 168 bp doublets. The most obvious difference lies in the deletion, in the former, of a 14 bp segment from one of the two related sequences. It is hypothesized that the IGS repeats are derived from the 336 bp elements and have been transposed to ribosomal cistrons from other genome fractions. The possible relations between these sequences and others with similar structural features found in other species are discussed.