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

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 (taf145 Delta TAND), in Saccharomyces cerevisiae by exploiting a red/white colony-sectoring assay. Our screen yielded several recessive nsl (Delta TAND 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 arise displayed synthetic lethal interactions with taf145 Delta TAND, indicating that TAND and TBP carry an overlapping but as yet unidentified function that is specifically required for transcriptional regulation.