IN-VITRO EVIDENCE FOR GROWTH-REGULATION OF TRANSFER-RNA GENE-TRANSCRIPTION IN YEAST - A ROLE FOR TRANSCRIPTION FACTOR (TF) IIIB70 AND TFIIIC

We report in vitro studies showing that tRNA gene transcription in yea st is down-regulated during the transition from logarithmic to station ary phase growth. Transcription in a postdiauxic (early stationary) ph ase extract of a wild-type strain decreased 3-fold relative to a log p hase extract. This growth stage-related difference in transcription wa s amplified to 20-fold in extracts of a strain containing a mutation ( pcf1-4) in the 131-kDa subunit of TFIIIC. The reduction in transcripti on activity in both wild-type and mutant postdiauxic phase extracts wa s correlated with a decrease in the amount of TFIIIB70, the limiting f actor in these extracts. However, the 3.7 +/- 0.5-fold decrease in amo unt of TFIIIB70 in mutant extracts does not, by itself, account for th e 20-fold decrease in transcription, Accordingly, transcription in the mutant postdiauxic phase extract could be reconstituted to a level eq ual to the mutant log phase extract by the addition of two components, TFIIIB70 and TFIIIC. Addition of TFIIIB70 increased transcription 10- fold, while a 2-fold effect of TFIIIC was seen at saturating levels of TFIIIB70. The data suggest that both TFIIIB70 and TFIIIC play a role in coordinating the level of polymerase III transcription with cell gr owth rate.