Mutations in the TATA-binding protein, affecting transcriptional activation, show synthetic lethality with the TAF145 gene lacking the TAF N-terminal domain in Saccharomyces cerevisiae

Abstract

The general transcription factor TFIID, which is composed of the TATA box-binding protein (TBP) and a set of TBP-associated factors (TAFs), is crucial for both basal and regulated transcription by RNA polymerase II. The N-terminal small segment of yeast TAF145 (yTAF145) binds to TBP and thereby inhibits TBP function. To understand the physiological role of this inhibitory domain, which is designated as TAND (TAF N-terminal domain), we screened mutations, synthetically lethal with the TAF145 gene lacking TAND (taf145ΔTAND), in Saccharomyces cerevisiae by exploiting a red/white colony-sectoring assay. Our screen yielded several recessive nsl (ΔTAND synthetic lethal) mutations, two of which, nsl1-1 and nsl1-2, define the same complementation group. The NSL1 gene was found to be identical to the SPT15 gene encoding TBP. Interestingly, both temperature-sensitive nsl1/spt15 alleles, which harbor the single amino acid substitutions, S118L and P65S, respectively, were defective in transcriptional activation in vivo. Several other previously characterized activation-deficient spt15 alleles also displayed synthetic lethal interactions with taf145ΔTAND, indicating that TAND and TBP carry an overlapping but as yet unidentified function that is specifically required for transcriptional regulation.