The Journal of Cell Biology, Vol 98, 954-962, Copyright © 1984 by The Rockefeller University Press
Phosphorylation of some chromosomal nonhistone proteins in active genes is blocked by the transcription inhibitor 5,6-dichloro-1-beta-D- ribofuranosylbenzimidazole (DRB)
E Egyhazi, A Pigon, A Ossoinak, M Holst and U Tayip
The distribution of rapidly phosphorylated chromosomal proteins between
chromosome I, chromosome II + III, chromosome IV, and nuclear sap including
the matrix was investigated in salivary gland cells of Chironomus tentans.
Chromosome IV, which carries most active nonribosomal genes in the cell,
was found to be enriched in four rapidly phosphorylated nonhistone
polypeptides (Mr = 25,000, 30,000, 33,000, and 42,000) in parallel with the
transcriptional activity rather than with the DNA content of the
chromosome. Also the histones H2A and H4 are rapidly phosphorylated but the
phosphorylation is proportional to the DNA content of each chromosome
sample. The 32P- labeled Mr = 42,000 polypeptide immunologically
cross-reacted with an antibody elicited against the transcription
stimulatory factor S-II isolated from Ehrlich ascites tumor cells
(Sekimizu, K., D. Mizuno, and S. Natori, 1979, Exp. Cell Res., 124:63-72).
In addition, indirect immunofluorescence studies on chromosome IV with
antisera against the stimulatory factor II revealed a selective staining of
the active gene loci. The incorporation of 32P into three chromosome IV
nonhistone polypeptides, especially into the Mr = 42,000 polypeptide, was
lowered by 70-85% shortly after administration of 5,6-dichloro-1-beta-D-
ribofuranosylbenzimidazole (DRB), a likely inhibitor of heterogeneous
nuclear RNA transcription at initiation level. The possibility of a causal
relationship between inhibited phosphorylation of chromosomal proteins and
blocked transcription of heterogeneous nuclear RNA genes by DRB is
discussed.
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