[Transcription of portions of chromosomes corresponding to regions of intercalary heterochromatin in Drosophila melanogaster cell cultures].

Labelled RNA preparations (total newly synthesized RNA, as well as stable cytoplasmic RNA) isolated from a cell culture of Drosophila melanogaster were hybridized in situ with polytene chromosomes. Apart from the nucleolus, in all cases the regions adjacent to he chromocentre in the polytene chromosomes and the intercalary heterochromatin regions in the X chromosome and the autosomes are the most intensively labelled. In the case of asynapsis of polytene chromosomes in heterozygotes the label is detected in a number of intercalary heterochromatin sites in one homologous only ("the asymmetrical label"). The same kind of radioactivity distribution in intercalary heterochromatin regions was observed after a hybridization of polytene chromosomes with cloned DNA fragments (Ananiev et al.,, 1978, 1979) coding for the abundant classes of messenger RNA (Ilyin et al., 1978) in cultured D. melanogaster cells. In some regions of intercalary heterochromatin which do not contain these fragments the "asymmetrical" type of labelled distribution is observed after hybridization with cell RNA. These results lead one to regard the intercalary heterochromatin regions as "nests" comprising different types of actively transcribable genes, the composition of each nest varying in different stocks of D. melanogaster.