Initiation inhibition and reinitiation of the synthesis of heterogeneous nuclear RNA in living cells

Abstract

THE nucleoside analogue 5,6-dichloro-1-β-D-ribofuranosyl-benzimidazole (DRB) inhibits the synthesis of heterogeneous nuclear RNA (hnRNA) at the initiation level in explanted salivary glands of Chironomus tentans, but does not interfere with the synthesis of ribosomal RNA and transfer RNA (refs 1–4). When the radioactive RNA precursors and the inhibitor are coincidently added to the glands the labelling of hnRNA transcripts produced by smaller transcriptional units is suppressed before that of the larger ones^2,3. If, however, the glands are pretreated with DRB, and the time of preincubation is sufficiently long, labelling of small as well as large hnRNA transcripts is equally eliminated, and the DNA template becomes depleted of nascent hnRNA chains^2–4. Important questions, arising from these findings, are whether DRB can be washed out from the cells, and whether a reinitiation of hnRNA synthesis can subsequently be achieved. This paper presents data which show that the initiation of the RNA synthesis resumes when glands pretreated with DRB are washed and replenished with inhibitor-free medium.