Modification of transcriptional activity induced by protein synthesis inhibitors in salivary gland cells of Chironomus thummi.

Uridine incorporation in salivary gland cells of Chironomus thummi may be increased by short treatments with cycloheximide, anisomycin or emetine. Accordingly, the rate of UTP incorporation in drug pre-treated permeabilized glands is higher than in control glands. Electrophoretical analyses indicate that when the aforementioned inhibitors are given to whole larvae, the synthesis of glandular giant-heterogeneous RNA and, to a higher extent, that of low molecular weight (4-5S) RNA, are enhanced, while nucleolar 38S pre-rRNA synthesis is generally depressed. On the contrary, when the inhibitors are directly applied to excised glands, the the synthesis of all RNAs, including the pre-ribosomal one, is higher than in control glands. These results suggest that the transcription of various RNA species in polytene cells of C. thummi appears to be specifically regulated by mechanisms in which newly synthesized proteins are involved. In addition, the response of nucleolar genes transcription to treatments with protein synthesis inhibitors seems to be dependent on the environmental conditions of the glands.