The influence of molting hormone on RNA synthesis in isolated polytene nuclei of Drosophila

Size and distribution of polyadenylic acid sequences in Drosophila polytene DNA and RNA

[3H]Poly(U) hybridizes very rapidly to polytene DNA from Drosophila hydei. When hybridization is performed at 30 degrees C in 2 X SSC to a large excess of DNA, 95% of the poly(U) becomes ribonuclease resistant. Also, complementary RNA transcribed in vitro from polytene DNA hybridizes to poly(U). 023--0.25% of the DNA is composed of (dA)-rich sequences and 0.23--0.31% of cRNA hybridizes to [3H]poly(U). The length of the (dA)-rich sequences on the DNA and cRNA is 40 nucleotides. The Tm values of these hybrids formed between DNA or cRNA-poly(U) is 45 degrees C. The poly(A) fragments from cytoplasmic RNA ranged from 80 to 170 nucleotides in lenght, and migrated in polyacrilamide gels as a broad peak. The average sizes of the poly(A) fragments from the poly(A)-containing RNA transcribed by nuclei isolated from salivary glands in vivo or in vitro were 40, 70, 170 and 70 nucleotides, respectively. Hybridization in situ of [3H]-poly(U) to chromosome squashes indicated that the (dA)-rich sequences are randomly distributed over the whole genome.

RNA synthesis by exogenous RNA polymerase on cytological preparations of chromosomes

Cytological preparations of Drosophila polytene chromosomes serve as templates for RNA synthesis carried out by exogenous RNA polymerase (Escherichia coli). Incorporation of labeled ribonucleoside triphosphates into RNA may be observed directly by autoradiography. Because of the effects of rifampicin, actinomycin D, ribonuclease, high salt, and the requirement for all four nucleoside triphosphates, we conclude that the labeling observed over chromosomes is due to DNA-dependent RNA polymerase activity. Using this method, one can observe RNA synthesis in vitro on specific chromosome regions due to the activity of exogenous RNA polymerase. We find that much of the RNA synthesis in this system occurs on DNA sequences which appear to be in a nondenatured state.