[Chromatin structure, heterochromatin, and transposable genetic elements--are they from one team?]. / Struktura khromatina, geterokhromatin i podvizhnye geneticheskie élementy--igroki odnoi komandy?

Gene content proved to be less than expected in completely sequenced eukaryotic genomes. Moreover, gene number differs only three times between such distant organisms as human and Drosophila. Hence it is likely that the essential functional and structural differences between the two species mostly depend on the regulation of gene activity than on the set and quality of genes themselves. New data demonstrate that changes in chromatin structure play a greater role in the fine gene activity regulation than considered before. R.B. Khesin had foresaw many chromatin functions that only recently came to be recognized. Khesin was interested in genome inconstancy over his last years. A higher content of several important chromosomal proteins was recently revealed in chromatin of transposable genetic elements (TGE). The possible role of TGE in chromatin organization in the nucleus is considered.

[Comparative analysis of the localization and mobility of retrotransposons in sibling species Drosophila simulans and Drosophila melanogaster]. / Sravnitel'nyi analiz lokalizatsii i podvizhnosti retrotranspozonov u vidov-bliznetsov Drosophila simulans i Drosophila melanogaster.

The distribution of four retrotransposon families (MDG1, MDG3, MDG4 and copia) on polytene chromosomes of different (from 9 to 15) Drosophila simulans strains is studied. The mean number of MDG1 and copia euchromatic hybridization sites (3 sites for each element) is drastically decreased in D. simulans in comparison with D. melanogaster (24 and 18 sites respectively). The mean number of MDG3 sites of hybridization is 5 in D. simulans against 12 in D. melanogaster. As for MDG4 both species have on the average about 2-3 euchromatic sites. The majority of MDG1 and copia and about a half of MDG3 euchromatic copies are localized in restricted number of sites (hot spots) on D. simulans polytene chromosomes. In D. melanogaster these elements are scattered along the chromosomes though there are some hot spots too. It appears that euchromatic copies of MDG1 and copia are considerably less mobile in D. simulans in contrast to D. melanogaster. Some common hot spots of retrotransposon localization in D. simulans and D. melanogaster were earlier described as intercalary heterochromatin regions in D. melanogaster. The level of interstrain variability of MDG4 hybridization sites is comparable in both species. Comparative blot-analysis of adult and larval salivary gland DNA shows that MDG1 and copia are situated mainly in euchromatic regions of D. melanogaster chromosomes. In D. simulans genome they are located mainly in heterochromatic regions underreplicated in salivary gland polytene chromosomes. There are interspecies differences in the distribution of retrotransposons in beta-heterochromatic chromosome regions.

[Cloning of segments of the Drosophila melanogaster genome using artificial chromosomes of the yeast Saccharomyces cerevisiae]. / Klonirovanie uchastkov genoma Drosophila melanogaster v iskusstvennykh khromosomakh drozhzhei Saccharomyces cerevisiae.

A partial genomic library from the Batumi L stock of Drosophila melanogaster was constructed using yeast artificial chromosomes as vectors. The DNA was restricted by Not1 and large fragments were inserted into the YAC5 vector. The size of cloned DNA varied from 90 to 500 kb. 48 random clones were characterized by in situ hybridization to the Batumi L polytene salivary gland chromosome. Single euchromatic sites of hybridization were detected for 27 clones; 11 clones revealed the main euchromatic hybridization site and several additional sites scattered along the chromosomes; 8 clones carried repeats which hybridized to chromocenter and other chromosomal sites; clones with 500 and 90 kb inserts originated from the Y chromosomes and nucleolus, respectively. The library is enriched by the repeated sequences related to the b-heterochromatin.

[Hoppel-family of mobile elements of Drosophila melanogaster, flanked by short inverted repeats and having preferential localization in the heterochromatin regions of the genome]. / Hoppel-semeistvo mobil'nykh élementov Drosophila melanogaster, flankirovannoe korotkimi invertirovannymi povtorami i imeiushchee aredpochtitel'nuiu lokalizatsiiu v geterokhromatinovykh oblastiakh genoma.

A mobile element (ME) having 91% homology with Dm1360 (Kholodilov et al., 1987) has been cloned from the Drosophila melanogaster genome and sequenced. The family of ME was designated hoppel. The members of this family are flanked by short inverted repeats likewise P, hobo and HB. The hoppel is hybridized with 10-30 euchromatic sites of polytene chromosomes of different Drosophila stocks. Abundant hybridization with heterochromatic regions of chromosomes-chromocenter, pericentric heterochromatin, the 4 chromosome and telomeres was observed in all stocks of D. melanogaster examined and in D. simulans. At least six genomic variants of ME differing in length of the central part were revealed. Hoppel possesses ARS activity similar to the P element. Two ME hoppel were shown to be arranged as a direct repeat in the recombinant phage.

[Distribution of Drosophila melanogaster mobile genetic elements along X-chromosome and autosomes]. / Raspredelenie mobil'nykh geneticheskikh élementov Drosophila melanogaster po dline X-khromosom i autosom.

The distribution along Drosophila melanogaster polytene X-chromosome and autosomes of 10911 in situ hybridization sites of a broad spectrum of copialike mobile elements is investigated. It is shown that against DNA content X-chromsomal cytological sections 14 + 15 and 16 + 17 contain much less mobile elements than other chromosomal regions. These X-chromosomal regions are also characterized both by significant decrease in the meiotic recombination frequencies and the amount of poly(dC-dA).poly(dG-dT) sequences which are capable to generate the Z form of DNA.

[A family of repeated sequences in Drosophila genome with telomeric localization: properties and polymorphism]. / Semeistvo povtoriaiushchikhsia posledovatel'nostei genoma drozofily, imeiushchee telomernuiu lokalizatsiiu: svoistva i polimorfizm.

The previously cloned Drosophila genome fragment Dm665 (2.4 kb) hybridizing with telomers on polytene chromosomes is a representative of the family of repeats, a part of which being organized in tandem clusters. The repeats are not transcribed in cell culture, are species-specific and represented in 200-250 copies per haploid genome. In natural and laboratory Drosophila lines polymorphism has been revealed with regard to homology with Dm665 in the telomeres.

[Mobile elements in Drosophila natural populations in Azerbaijan]. / Mobil'nye élementy drozofily v prirodnykh populiatsiiakh Azerbaidzhana.

The distribution of four genome DNA fragments containing different mobile elements in chromosomes of Drosophila melanogaster individuals from Azerbaijan coast and mountain populations was studied. The average copy number of each element was shown to be approx. equal in both populations. Sites of preferential localization, where the elements were present in no less than in half of individuals could be revealed in each population for all the elements. A part of these sites coincided with regions of intercalary heterochromatin, the number of such coincidences being larger in mountain populations. The copy number of the mobile elements under study in X-chromosomes of individuals from natural populations as well as from laboratory strains was less than in autosomes. X-chromosomes of different individuals differed in mobile elements' localization more than autosomes. It was assumed that peculiarities of mobile elements' distribution in X-chromosome could reflect the effect of decondensed structure of chromatin in male X-chromosome on the transposition of mobile elements.

[The variability of the telomeric and of a number of internal regions of Drosophila chromosomes according to the intensity of hybridization in situ with labelled probes]. / Variabel'nost' telomernykh i riada vnutrennikh raionov khromosom drozofily po intensivnosti gibridizatsii in situ s mechenymi zondami.

Cloned Drosophila DNA fragments containing telomere-specific sequences have been hybridized in situ. It is found that intensity of their hybridization with telomeres greatly varies in different nuclei of the same salivary gland. This phenomenon is also observed for internal sites where some mobile elements included in several DNA fragments under investigation are located. Within each nucleus different regions are hybridized non-uniformly as well. It is suggested that these phenomena can be explained by varying polytenization in telomeres and some internal chromosomal regions.

[Effect of the deficiency of histone structural genes on their amount in Drosophila]. / Vliianie nekhvatki gistonovykh genov na ikh kolichestvo u drozofily.

The amount of histone structural genes was determined in heterozygotes for two different deficiencies of the histone locus of the 2nd chromosome. In case one chromosome lacks histone genes, the number of histone structural genes in the normal homologous chromosome is likely to increase by means of magnification and compensation in the same way as in the case of rRNA genes.

[Replication and transcription in Drosophila cells treated with novobiocin]. / Replikatsiia i transkriptsiia v kletkakh drozofily, obrabotannykh novobiotsinom.

The effect of novobiocin on replication and transcription in the cells of Drosophila was investigated by incorporation of 3H-thymidine and 3H-uridine into the diploid cell nuclei of the ganglia and imaginal discs, as well as into the polythene nuclei of the salivary gland cells of the Drosophila larvae. An inhibitory effect of the antibiotic on these processes was shown. Possible mechanisms of the novobiocin effect on DNA and RNA synthesis are discussed.

[Chromosome structure, histones and gene activity in Drosophila]. / Struktura khromosom, gistony i aktivnost' genov u drozofily

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.

[A comparison of bacterial RNA-polymerase RNA synthesis on polytene Drosophila chromosomes with transcription in living cells]. / Sravnenie sinteza RNK bakterial'noi RNK-polimerazoi na politennykh khromosomakh drozofily s transkriptsiei v zhivykh kletkakh

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.