THE COCKAYNE-SYNDROME-B PROTEIN, INVOLVED IN TRANSCRIPTION-COUPLED DNA-REPAIR, RESIDES IN AN RNA-POLYMERASE II-CONTAINING COMPLEX

Transcription-coupled repair (TCR), a subpathway of nucleotide excisio n repair (NER) defective in Cockayne syndrome A and B (CSA and CSB), i s responsible for the preferential removal of DNA lesions from the tra nscribed strand of active genes, permitting rapid resumption of blocke d transcription, Here we demonstrate by microinjection of antibodies a gainst CSB and CSA gene products into living primary fibroblasts, that both proteins are required for TCR and for recovery of RNA synthesis after UV damage in viva but not for basal transcription itself, Furthe rmore, immunodepletion showed that CSB is not required for in vitro NE R or transcription. Its central role in TCR suggests that CSB interact s with other repair and transcription proteins, Gel filtration of repa ir-and transcription-competent whole cell extracts provided evidence t hat CSB and CSA are part of large complexes of different sizes, Unexpe ctedly, there was no detectable association of CSB with several candid ate NER and transcription proteins, However, a minor but significant p ortion (10-15%) of RNA polymerase Pi was found to be tightly associate d with CSB. We conclude that within cell-free extracts, CSB is not sta bly associated with the majority of core NER or transcription componen ts, but is part of a distinct complex involving RNA polymerase II. The se findings suggest that CSB is implicated in, but not essential for, transcription, and support the idea that Cockayne syndrome is due to a combined repair and transcription deficiency.