Nhp6, an HMG1 protein, functions in SNR6 transcription by RNA polymerase III in S-cerevisiae

Nhp6A and Nhp6B are HMG1-like proteins required for the growth of S. cerevi siae at elevated temperatures. We show that the conditional lethality of an nhp6 strain results from defective transcription of SNR6 (U6 snRNA) by RNA polymerase III. Overexpression of U6 snRNA or Brf1, a limiting component o f TFIIIB, and an activating mutation (PCF1-1) in TFIIIC were each found to suppress the nhp6 growth defect. Additionally, U6 snRNA levels, which are r educed over 10-fold in nhp6 cells at 37 degreesC, were restored by Brf1 ove rexpression and by PCF1-1. Nhp6A protein specifically enhanced TFIIIC-depen dent, but not TATA box-dependent, SNR6 transcription in vitro by facilitati ng TFIIIC binding to the SNR6 promoter. Thus, Nhp6 has a direct role in tra nscription complex assembly at SNR6.