Rpb1 Sumoylation in Response to UV Radiation or Transcriptional Impairment in Yeast

Abstract

It has been well known that in response to DNA damage that blocks transcription elongation, Rpb1, the largest subunit of RNA polymerase II, is ubiquitylated and subsequently degraded in mammalian and yeast cells. Here we show that in response to UV radiation or impairment of transcription elongation, Rpb1 is also covalently modified by the Small‐Ubiquitin‐like Modifier (SUMO) in yeast cells. Ubc9, an E2 SUMO conjugase, and Siz1, an E3 SUMO ligase, play important roles in Rpb1 sumoylation. K1487, which is located in the acidic linker region between the C‐terminal domain and the globular domain of Rpb1, is the major sumoylation site. Rpb1 sumoylation is not affected by its ubiquitylation, and vice versa, indicating that the two processes do not crosstalk. Abolishment of Rpb1 sumoylation at K1487 does not affect transcription elongation or transcription coupled repair (TCR) of UV‐induced DNA damage. However, deficiency in TCR enhances UV‐induced Rpb1 sumoylation, presumably due to the persistence of transcription‐blocking DNA lesions in the transcribed strand of a gene. Remarkably, abolishment of Rpb1 sumoylation at K1487 enhances UV‐induced phosphorylation of Rad53, especially in TCR‐deficient cells, suggesting that the sumoylation may play a role in restraining the DNA damage checkpoint response caused by transcription‐blocking lesions.