[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.