Rapidly phosphorylated histone-like proteins are modulated in the course of transcription block by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole.

A putative histone H2A and H4 protein with posttranslationally added and covalently linked phosphate group(s) have been found in salivary gland cells of Chironomus tentans. The phosphate moieties possess a rapid turnover rate and the incorporation of 32P reaches steady-state level within 5 to 10 min of incubation. The H2A-like protein incorporates twice as much label as the H4-like one. The core histones H2B and H3 are not measurably phosphorylated under identical experimental conditions. The administration of the nucleoside analogue 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB), a likely inhibitor of transcription initiation, rapidly modulates the phosphorylation of H2A- and H4-like proteins. The incorporation of 32P into the H2A-like phosphoprotein is enhanced by up to 180% after 3 to 10 min of preincubation with DRB but the rise in phosphorylation is of a transient character. The phosphorylation of H4-like protein is affected somewhat later than that of H2A but the stimulatory effect persists even after a longer pretreatment with DRB. If the elongation inhibitor alpha-amanitin replaces DRB in similar experiments no significant effect on histone phosphorylation can be registered. The results are discussed in relation to the possibilities that there is a cause and effect relation between the rapid modulation of phosphorylated putative histone proteins and the repression of gene activity or condensation of active chromatin.