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Biomedical subjects

R B Khesin

Publications and source records attributed to R B Khesin.

10 recordsLinked to original sources
PubMed1978

Influence of deficiency of the histone gene-containing 38B-40 region on X-chromosome template activity and the white gene position effect variegation in Drosophila melanogaster.

The deficiency of the 38B-40 region containing histone genes in one of the 2nd chromosomes of D. melanogaster triploid intersexes increases the template activity of X-chromosomes both in vivo and in vitro without noticeably affecting autosome activity. This deficiency in the heterozygous state inhibits the variegated position effect of the white gene in the T(1;3)Wvco translocation in diploid females and males, but not affect their rate of development. The variegation suppressor Su(var)hg-1 not only suppress the gene position effect in diploid flies, but also increases the template activity of X-chromosomes in triploid intersexes. The results are discussed with respect to the dependence of gene activity on the structure of chromosomes (density of DNP packing).

Animals↗
PubMed1976

The influence of mutations upon the synthesis of RNA polymerase subunits in Escherichia coli cells.

The influence of mutations in structural genes of beta and beta subunits of RNA polymerase upon the synthesis of these subunits in E. coli cells have been investigated. An amber-mutation ts22 in the beta subunit gene decreases the intracellular concentration of this subunit and the rate of its synthesis. At the same time the concentration and the rate of beta subunit synthesis is increased. These suggest the compensatory activation of the RNA polymerase operon that takes place under the conditions of shortage of one of the subunits. Reversions as well as more effective suppression of ts22 amber mutation, achieved by streptomycin addition, substitution of su2 by sul, or by specific mutations, result in a rise of beta and drop of beta subunit concentration and synthesis in ts22 mutant. TsX missense-mutation in the beta subunit gene alters the properties of the enzyme increasing, at the same time, the concentration and the rate of synthesis of both beta and beta subunits, particularly at a nonpermissive temperature. This points to an inversely proportional relationship between the rate of synthesis of RNA polymerase subunits and the total intracellular activity of the enzyme. Extra subunits are rapidly degraded in ts22 and tsX mutants. The whole complex of our data and those of others suggest that the regulation of the synthesis of RNA polymerase subunits is accomplished by interaction of a negative and a positive mechanisms of regulation which include not only activators and repressors but the enzyme itself as well.

DNA-Directed RNA Polymerases↗
PubMed1976

Comparison of in vivo and in vitro RNA synthesis on polytene chromosomes of Drosophila.

A comparative radioautographic study of the RNA precursors incorporation on polytene chromosomes of Drosophila in vivo in the cells of salivary glands, and in vitro during incubation of E.coli RNA polymerase on slides with fixed chromosomes was performed.--The pattern of in vivo 3H-uridine incorporation on different sections of the chromosomes drastically differed from the in vitro 3H-UTP incorporation which seems to be much more related to DNA content of the individual small sections. In both cases puffing of the loci resulted in the increase of RNA synthesis but in vitro only 2-3 fold and in vivo much more. Hence, RNA synthesis in vitro was unspecific and did not reflect the in vivo RNA synthesis.--On the other hand, E.coli RNA polymerase completely mimics in vitro the dosage compensation phenomenon making twice as much RNA on one X-chromosome of males (1X2A) as on each of X-chromosomes of diploid (2X2A) and triploid (3X3A) females and super-females (3X2A), and the intermediate amount of RNA on each of X-chromosomes of intersexes (2X3A). It is suggested that the differences in the in vitro template activity of X-chromosomes of cells with different X:A ratio are due to different extent of condensation of their deoxyribonucleoprotein (DNP). Yet, both male and each of female X-chromosomes bind the same amount of thymus histone FI labelled with fluorochrome which indicates that they contain the same amount of "open" regions with exposed chromosomal DNA accessible to external proteins.--On the basis of these observations a hypothesis is put forward which suggests that RNA transcription in animal chromosomes is regulated at two levels by different mechanisms; the first one controls the extent of condensation of DNP of genetic loci and determines their competence to the second mechanism which involves the action of gene-specific activator proteins. According to this hypothesis the phenomenon of dosage compensation of sex-linked genes is due to decondensation of DNP of male X-chromosome which renders its loci twice as responsive to activators as compared to the same loci in females.

Animals↗
PubMed1975

[Current problems of molecular genetics].

Some problems of molecular genetics are considered. A special attention is paied to enzymology of genetic processes, in particular, to the mechanism of DNA replication, gene ingeneering and the structure and activity regulation mechanisms of genetic loci in higher organisms.

Animals↗
PubMedDate not supplied

[Chromosome structure, histones and gene activity in Drosophila].

The problem to be reviewed in this study concerns the mechanism of regulation of gene activity relied on the structural changes of the chromatin. The role of histones in the regulation of transcription is discussed on the basis of the results obtained by the authors and literature data. In particular, the results are presented of the investigations of decrease of the histone amount in the cell nucleus using the deficiency of histone structural genes. This leads both to the increase of the X-chromosome template activity and the inhibition of variegated position effect. The latter is also inhibited by feeding of larvae with T2-DNA. It is supposed that the chromatin structure is a mechanism of epigenetic changes and the gene inactivation due to the position effect inherited in cell lineages in an example of such epigenetic changes.

Animals↗
PubMedDate not supplied

[Synthesis of RNA polymerase subunits in Escherichia coli mutants].

The influence of mutations in structural genes of beta- and beta'-subunits of RNA polymerase upon the synthesis of these subunits in E. coli cells have been investigated. An amber-mutation ts22 in the beta-subunit gene decreases the intracellular concentration of this subunit and the rate of its synthesis. At the same time the concentration and the rate of beta'-subunit synthesis is increased. These facts suggest the compensating activation of the synthesis of RNA polymerase subunits that takes place under the conditions of deficiency in one of the subunits. Reversions, as well as more effective suppression of ts22 amber-mutation achieved by streptomycin addition or substitution of su2 by sul result in a rise in the concentration and the rate of beta-subunit formation. This is accompanied by a drop in the concentration and the role of beta'-subunit synthesis. tsX missense motation in the beta'-subunit gene alters the properties of the enzyme increasing at the same time the concentration and the rate of synthesis of both subunits, particularly at nonpermissive temperature. This points to an inversely proportional relationship between the rate of synthesis of RNA polymerase subunits and total intracellular activity of the enzyme. Extra subunits are rapidly degraded in ts22 and tsX mutants.

DNA-Directed RNA Polymerases↗