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Sense and antisense transcripts of suffix and F element were detected at different stages of Drosophila development. A short RNA, similar in size to the full-length suffix transcript, was also found. It was suggested that it could originate from the master copy of the element. Though transcription pattern of these elements changed during the development, transcription remained symmetrical. These data indicate that formation of dsRNA in the cells and triggering of the RNA interference mechanisms are possible at all stages of Drosphila development. Analysis of total RNA samples from all stages of Drosophila development showed that 21- to 25-nt long suffix--specific small interfering RNAs (siRNA), the obligatory products of the RNA interference, were detected only in pupae. Thereafter, RNA interference mechanisms are developmentally regulated and the formation of dsRNA is necessary but not sufficient for launching this potent and specific machinery of post-transcription silencing.

RNA preparations synthesized in vitro were used to study the influence of RNA interference on the Kruppel gene activity in Drosophila embryos. RNA complementary in parallel orientation to the mRNA fragment proved to induce the development of Kruppel phenocopies. The data obtained indicate that mechanisms of specific regulation of gene activity exist in Drosophila cells, which are sensitive to the formation of both parallel and antiparallel RNA-RNA duplexes that include mRNA of the corresponding gene.

Transcripts of the cut locus were localized in Drosophila embryos with use of nonradioactive in situ hybridization. DIG-labeled probes were generated from two locus regions located at position -130. Distal and proximal regions were found to be transcribed in the same tissues throughout embryogenesis. As only the proximal region transcript was detected, the conclusion was made that two or more various transcripts derived from different regions of the locus and under common control, are present simultaneously in the embryonic cells.

Data on molecular analysis of the insertion sites of nine random copies of burdock retrotransposon are presented. The 12-bp consensus sequence of the insertion sites, YNNUTUTUYAYA (Y-pyrimidine; U-purine), was determined. Homology between the burdock sequence and ribosomal genes was revealed. Three copies of this element were located within the region of ribosomal repeats: one copy in the 18S RNA gene, and two copies in the same intergenic spacer region, in the so-called Alu-repeats of Drosophila, in different copies of ribosomal genes.

Nineteen DNA clones, containing copies of the suffix element retroposon of the Drosophila genome and produced by a polymerase chain reaction (PCR), were sequenced. Insertions of the copies in both orientations into microsatellite sequences (CAACA)n/(TGTTG)n and (TTTGT)n/(CACAAA)n were revealed. It was found that, if the microsatellite sequence has both a decanucleotide GCGGCCCGGG (GC-box) and a colinear alternating sequence (A)5(T)4(A)3(T)2(A)1(t)n (AT-box), the insertion of the suffix occurs in only one orientation. It is suggested, that in such apparently heterochromatic sequences, suffix element copies and probably some other retroposons can be inserted a particular orientation by means of site-specific recombination. An approach to analysis of the molecular organization of such sequences is proposed.