Ubiquitination of RNA polymerase II large subunit signaled by phosphorylation of carboxyl-terminal domain

A sensitive assay using biotinylated ubiquitin revealed extensive ubiquitin ation of the large subunit of RNA polymerase II during incubations of trans cription reactions in vitro. Phosphorylation of the repetitive carboxyl-ter minal domain of the large subunit was a signal for ubiquitination. Specific inhibitors of cyclin-dependent kinase (cdk)-type kinases suppress the ubiq uitination reaction. These kinases are components of transcription factors and have been shown to phosphorylate the carboxyl-terminal domain. In both regulation of transcription and DNA repair, phosphorylation of the repetiti ve carboxyl-terminal domain by kinases might signal degradation of the poly merase.