GENETIC TESTS OF THE ROLE OF ABF1P IN DRIVING TRANSCRIPTION OF THE YEAST TATA BOX BINDNG PROTEIN-ENCODING GENE, SPT15

In this report we describe studies which utilized yeast strains bearin g gain and loss of function alleles of ABF1 in order to attempt to dir ectly implicate Abf1p in modulating transcription of the TBP-encoding gene, SPT15, in vivo. We found that overexpression of Abf1p in a yeast cell increased transcription of the TBP-encoding gene and that this s timulation depended upon the exact sequence of the Abf1p binding site (ABF1) present in the gene. Further, in a yeast strain expressing a te mperature sensitive form of Abf1p, occupancy of the chromosomal ABF1 s ite in the TBP-encoding gene was immediately lost following a temperat ure shift. Both results suggest that Abf1p drives transcription of the TBP-encoding gene. Surprisingly though we found that continuous ABF1 cis-element occupancy by Abf1p was not acutely required for normal lev els of transcription of either the TBP-encoding gene or other ''Abf1p- driven'' genes tested. We propose a model to explain these results and suggest mechanisms by which Abf1p could activate gene transcription.