Inhibition of transcription selectively reduces the level of ubiquitinated histone H2B in chromatin.

The effect of inhibiting transcription and/or replication on the steady state levels of the ubiquitinated histone isoforms was investigated. We show that treatment of chinese hamster ovary (CHO), monkey kidney (COS), human endometrial carcinoma (Hec-50 and Ishikawa) cells with actinomycin D and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole, inhibitors of heterogeneous nuclear RNA synthesis, selectively reduced the levels of ubiquitinated (u) H2B, but not uH2A, uH2A.Z, polyubiquitinated H2A or a novel ubiquitinated histone species, in the chromatin of these cells. The level of the ubiquitinated histones was not affected when synthesis of DNA was arrested. These results show that, in general, maintenance of the levels of uH2B in chromatin is dependent upon ongoing transcription.