Nhp6p and Med3p regulate gene expression by controlling the local subunit composition of RNA polymerase II

Abstract

In this project, the Split-Ubiquitin system was used to isolate S. cerevisiae proteins that interacted with the non-histone chromosomal protein Nhp6p. The ZDS1 gene was utilized to study their chromosomal co-localization. Nhp6p, Med3p and the essential RNA polymerase II subunit Rpb2p were found at the entire ZDS1 locus, while Rpb4p was found at the ZDS1 promoter only, suggesting that the RNA Pol II that had transcribed ZDS1 was lacking the dissociable Rpb4p subunit. The deletion of NHP6 reduced binding of Rpb4p to the ZDS1 promoter, while the deletion of MED3 allowed Rpb4p to enter the ZDS1 open reading frame, indicating that Nhp6p loaded Rpb4p onto RNA Pol II at the ZDS1 promoter, while Med3p prevented ZDS1 promoter clearance of RNA Pol II that contained Rpb4p. Therefore, Nhp6p and Med3p repressed transcription of ZDS1 by controlling the local subunit composition of RNA Pol II.