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Biomedical subjects

R Tsanev

Publications and source records attributed to R Tsanev.

At least 55 records · Page 3Linked to original sources
PubMed1981

Nonprotamine nucleoprotein ultrastructures in mature ram sperm nuclei.

Nuclei from mature ram spermatozoa were treated with a solution of 0.25 M 2-mercaptoethanol, 2 M NaCl, 4 to 8 M urea to dissociate protamines and some other proteins from DNA. The material remaining after such a treatment was spread for electron microscopy in the microcentrifugation chamber. Two types of structures were observed determined by proteins of nonprotamine nature. The first type was represented by protein bodies of an irregular ringlike shape to which DNA fibers were anchored to form a network. This structure determines the shape of the sperm head and may correspond to the nuclear skeleton described in somatic cells. The second type of structures were chromatin fibers containing beads of approximately nucleosomal size. These rough fibers were unevenly distributed in the nucleus and were much less frequent than the smooth fibers usually observed. Both types of structures were determined by unusually firmly bound proteins. They were resistant not only to the reduction of disulfide bonds and to high salt and urea concentrations but also to 2% sodium dodecysulfate and to 5 M guanidine chloride. These results show that apart from packing of DNA in a nucleoprotamine complex, two levels of DNA organization can be observed in the ram sperm nucleus: the first level consists of two kinds of DNA fibers (smooth and rough); in the second level of DNA is organized in domains fixed by a proteinous nuclear skeleton.

Animals↗
PubMed1980

Histone exchange in chromatin of hydroxyurea-blocked Ehrlich ascites tumour cells.

It is well established that DNA and histone synthesis are tightly coupled. Nevertheless, these two processes can be partially uncoupled by drugs specifically inhibiting protein or DNA synthesis, and also during n-butyrate-induced differentiation of Friend cells. The fate of the histones synthesized in the absence of DNA synthesis is unknown; they could be: (1) degraded without joining chromatin; (2) deposited on chromatin as extra histones; or (3) replace original chromatin histones. The only data concerning this problem are a recent report supporting the second possibility. We present evidence here in favour of the third possibility by showing that the histones synthesized in the absence of DNA synthesis enter chromatin and become organized in nucleosomes.

Animals↗
PubMed1980

Salt-induced structural changes in nucleosomes.

Ehrlich ascites tumor (EAT) nucleosomes treated with increasing NaCl concentrations were analyzed by sucrose density gradient centrifugation. Two events were found to take place in the course of the salt treatment: a) increasing amounts of nucleosomes dissociated into free DNA and protein in the interval 0.6M-1.5M NaCl, and b) the sedimentation coefficient of the nucleosomes decreased from 11S to 8S in the interval 0.6M - 1M NaCl. This decrease was not caused by loss of protein and was fully reversible upon slow and gradual lowering of the ionic strength. This shows that before dissociation of the protein core from DNA, nucleosomes undergo a structural transition. The electron microscopic observations revealed that it consisted in detachment of the ends of nucleosomal DNA from the protein core. It is suggested that an arginine-rich domain in the protein core exists, which holds more tightly the central part of the nucleosomal DNA, while its ends are relatively loosely bound to lysine-rish domains.

Animals↗
PubMed1980

A comparison of histone variants in different rat tissues.

The histone patterns of rat liver, spleen, kidney and brain were compared by means of a two-dimensional electrophoresis in the presence of Triton X-100. In addition, a two-step procedure was introduced for quantitative estimation of different histone variants. Tissue differences wee found in the relative content of the different variants of H2a, H3 and the subfraction H1O. It was also found that the high salt induced H2a specific proteolytic activity was very high in spleen, very low in liver and kidney and absent in brain.

Animals↗
PubMed1980

Tissue specificity of tightly bound non-histone chromosomal proteins.

Non-histone chromosomal proteins with high affinity for DNA were isolated from three different rat tissues (liver, spleen and kidney) and were analyzed by SDS-polyacrylamide gel electrophoresis. Each tissue showed a characteristic pattern of missing protein bands and in addition contained at least one unique band. Quantitative differences between the common bands were also observed.

Animals↗
PubMed1980

Metabolically labile nonhistone proteins of chromatin.

In a previous paper in this journal [Djondjurov, L., Ivanova, E. and Tsanev, R. (1979) Eur. J. Biochem. 97, 133-139], we showed that a nuclear fraction released from chromatin under a mild nuclease digestion contained an increased amount of hnRNA and the bulk of nonhistone proteins with a high metabolic rate. The present investigation has revealed that the nonhistone proteins of this fraction could be divided into three distinct metabolic groups. The first group consists of proteins with a fast turnover rate (mean half-life 30 min) which migrate into chromatin immediately after their synthesis. These proteins are predominantly acid-soluble and have relatively high molecular weights. The second group includes proteins which migrate to the nucleus more slowly and metabolize with a moderate turnover rate (mean half-life 5 h). The third group contains proteins with a more conservative metabolic behaviour. In experiments with actinomycin D it was found that the bulk of the nonhistone proteins of this fraction are not real components of the chromatin but belong to the protein moiety of heterogeneous nuclear ribonucleoprotein particles associated with chromatin.

Animals↗
PubMed1980

Nucleosomes and nonribosomal RNA transcription in early mouse embryo. An electron microscopic study.

Zygotes from hyperovulated albino-mice isolated during the first several cleavages were spread according to the method of Miller and Bakken [28] in the presence and in the absence of Joy or in the presence of Sarcosyl. Our results show that: 1. already before the first division of the mouse zygote all chromatin is organized in nucleosomes, 2. nonribosomal RNA transcription starts during the first divisions, 3. chromatin fibers associated with nonribosomal RNA transcription have a nucleosomal structure and 4. the use of detergent Joy may destroy the nucleosomes of some chromatin fibers.

Animals↗
PubMed1979

The use of pronase for electron microscopy of protein-complexed DNA.

A method is described which demonstrates the posibility of visualizing protein-complexed DNA by using pronase for both deproteinization and spreading of DNA for electron microscopy. The results show that proteolytic digestion is complete even under conditions of short formaldehyde fixation and pronase is an excellent substitute for cytochrome c for spreading of DNA. The pronase method is successfully applied to virions, native and partially denatured chromatin. The procedure is highly advantageous because it does not require preliminary isolation of DNA, can be applied to microamounts of material and permits the visualization of partial denaturation of DNA in chromatin.

Animals↗
PubMed1979

Two chromatin fractions with different metabolic properties of non-histone proteins and of newly synthesized RNA.

Digestion of chromatin with micrococcal nuclease under mild conditions results in the release of a minor chromatin fraction showing an increased RNA and non-histone protein content, a fast turnover of the non-histone proteins and the presence of rapidly labelled heterogeneous nuclear RNA (hnRNA) with half-life of about 20 min. Further digestion of the chromatin leads to the elimination of about 19% of the initial chromosomal DNA, thus leaving a second chromatin fraction relatively resistant to nuclease attack. This fraction has a low protein and RNA content and contains only metabolically stable non-histone proteins. No differences in the histone complement of the two fractions was found except for a 40% deficiency of H1 in the minor fraction.

Animals↗
PubMed1978

Chromosomal proteins in hepatocarcinogenesis.

The chromosomal proteins of rat liver were studied by SDS-gel electrophoresis during the process of nitrosomorpholine-induced hepatocarcinogenesis, in the primary hepatomas thus obtained, and in their metastases. It was found that an increased proteolytic activity was present in liver homogenates from carcinogen-fed animals which caused differences between the nonhistone chromosomal proteins of control and carcinogen-treated livers. These differences disappeared in the presence of the protease inhibitor PMSF. In the primary hepatomas slight quantative changes were observed: an increased amount of two proteins of 43000 and 63000 daltons molecular weight, respectively, and a decrease in the histone subfraction H 1 degrees. In the metastases both quantative and qualitative differences were detected: a strong decrease in the protein bands corresponding to the contractile proteins alpha-tubulin, beta-tubulin, and actin; an increased content of the 63000 dalton protein; the appearance of new proteins of approximately 60000, 90000, and 120000 daltons molecular weight, and the complete disappearance of histone H 1 degrees.

Animals↗
PubMed1978

Metabolically stable non-histone chromosomal proteins in growing maize roots.

DNA and non-histone chromosomal proteins (NHCP) of meristematic cells of maize primary roots were double labelled in vivo with [3H]- or [14C] thymidine and [14C]- or [3H]-tryptophan respectively. The ratio of labelled tryptophan to labelled DNA was followed during the transition of the meristematic cells of the root tip into the distal zones of finally differentiated cells. It was found that only 20% of the newly synthesized NHCP in the proliferating cells were turned over, while the rest were preserved and found as metabolically stable proteins in the zone of final differentiation. This result is consistent with the hypothesis that some NHCP remain permanently associated with chromatin of non-dividing differentiated cells in order to maintain the genomic characteristics of a given cellular type.

Cell Division↗
PubMed1977

[Uroporphyrinogen-I-synthetase in erythrocytes in acute intermittent porphyria].

The primary genetic defect in acute intermittent porphyria is a decreased uroporphyrinogen I-synthetase [EC.4.3.1.8] activity. As a beginning of a genealogical study of the known families with members suffering from this disease in the People's Republic of Bulgaria, the red cell uroporphyrinogen I-synthetase was determined in 3 families by the method of Mandel et al [8]. Except for the three propositi, an enzyme deficiency was established in 3 latent carriers of the pathological gene, two of whom had normal values of the urinary epsilon-aminolevulinic acid and porphobilinogen. The determination of red cell uroporphyrinogen I-synthetase proved to be a valuable parameter for revealing the latent AIP.

Adolescent↗