Yeast Rpb9 plays an important role in ubiquitylation and degradation of Rpb1 in response to UV induced DNA damage

Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803

^* To whom correspondence should be addressed. Email: shli{at}lsu.edu.

	Abstract

Rpb9, a nonessential subunit of RNA polymerase II (Pol II), has multiple transcription-related functions in yeast, including transcription elongation and transcription coupled repair (TCR). Here we show that, in response to UV radiation, Rpb9 also functions in promoting ubiquitylation and degradation of Rpb1, the largest subunit of Pol II. This function of Rpb9 is not affected by any pathways of nucleotide excision repair, including TCR mediated by Rpb9 itself and by Rad26. Rpb9 is composed of 3 distinct domains: the N-terminal Zn1, the C-terminal Zn2 and the central linker. The Zn2 domain, which is dispensable for transcription elongation and TCR functions, is essential for Rpb9 to promote Rpb1 degradation, whereas the Zn1 and linker domains, which are essential for transcription elongation and TCR functions, play a subsidiary role in Rpb1 degradation. Co-immunoprecipitation analysis suggests that almost the full-length of Rpb9 is required for a strong interaction with the core Pol II: deletion of the Zn2 domain causes dramatically weakened interaction, whereas deletion of the Zn1 and linker resulted in undetectable interaction. Furthermore, we show that Rpb1, rather than the whole Pol II complex, is degraded in response to UV radiation, and the degradation is primarily meditated by the 26S proteasome.