PubMed Health⌕ Search

Biomedical subjects

R B Khesin

Publications and source records attributed to R B Khesin.

At least 19 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↗
PubMed1974

[A comparison of bacterial RNA-polymerase RNA synthesis on polytene Drosophila chromosomes with transcription in living cells].

The incorporation of 3H-uridine in different regions of polytene chromosomes in live cells of the Drosophila melanogaster salivary glands was compared with the incorporation of 3H-UTP in the same regions under the incubation of cytological preparations of these chromosomes with the E. coli RNA polymerase. The label distribution by regions was compared with the DNA content in them. Individual regions of chromosomes differ by 3H-uridine incorporation in live cells to a much greater extent than by 3H-UTP incorporation in vitro under the incubation with a non-homologous enzyme. RNA synthesis in an exogenous enzyme depends on the DNA content in different chromosome regions to a much greater extent than RNA synthesis in vivo. The correlation of label distribution after 3H-uridine incorporation in live cells and after RNA synthesis in vitro on the preparations by the bacterial RNA polymerase is, correspondingly, very low. This enzyme forms, however, RNA's on puffs 2-3 times more actively than on the same regions in non-puffing state but this difference is dozens of times greater in live cells. RNA synthesis in vitro is, thus, non-specific and does not correspond practically to the intensity of RNA synthesis on the same chromosome regions in live cells. At the same time, as in live cells, the E. coli enzyme synthesizes twice more RNA on the single X-chromosome of males (1X2A) than on each of X-chromosomes of diploid (2X2A) and triploid (3X3A) females or superfemales (3X2A), whereas in intersexes (2X3A) X-chromosomes display intermediate template activity. Thus, RNA synthesis by a heterologous enzyme in vitro does not differ by this index from the synthesis in live cells. It is suggested that differences in the template activity of X-chromosomes in vitro depending on the sex index (X : A) are due to different degree of DNP condensation in these chromosomes. In spite of differences in the degree of condensation, the male X-chromosome binds on the fixed preparation approximately the same amount of thymus histone F1 carrying fluorochrome as each of two female X-chromosomes. Hence, there is no sharp difference between the male and female X-chromosomes by the number and length of DNA regions accessible for interaction with exogenous proteins. On the basis of the data obtained, a hypothesis about two levels and, respectively, two mechanisms of control gene activity in animal chromosomes is considered. The first mechanism is, supposedly, based on decondensation of DNP appears to result in that the same proteins-regulators in the same amount activate corresponding genes in X-chromosome in males twice more strongly than in females.

Animals↗
PubMedDate not supplied

[R-factors of mercury resistance in bacteria isolated in the mercury-antimony deposit region].

Most of bacterial cells in soil samples taken from a mine at the Khaidarkan mercury-antimony deposit (Kirghiz SSR) proved to contain R-plasmids with determinants of mercury resistance (HgCl2). Plasmids had a high molecular mass (approximately 10(8], though some deviated substantially from this size; at least part of them were transmissible. Many Hgr bacteria also showed an increased resistance to antimony (SbCl3), but no relation could be found between this character and the plasmids. Bacteria from soil samples taken at different distances from the mine were virtually devoid of Hgr plasmids: saturation of bacteria with Hgr factors is maintained by selective pressure action only within regions with high concentration of poison. Hgr plasmids at the Khaidarkan deposit were also found in enteric bacteria isolates from the gut of Mus musculus mice and Bufo viridis toads. Some bacterial plasmids from animals carried, apart from Hgr, antibiotic resistance determinants (Tcr, Cmr, Smr), i.e. were multiple resistance factors. These plasmids often displayed intrinsic instability and lost resistance determinants when conjugationally transferred to some E. coli strains.

Animals↗