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 bearing gain and loss of function alleles of ABF1 in order to attempt to directly 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 stimulation depended upon the exact sequence of the Abf1p binding site (ABF1) present in the gene. Further, in a yeast strain expressing a temperature sensitive form of Abf1p, occupancy of the chromosomal ABF1 site in the TBP-encoding gene was immediately lost following a temperature 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 levels 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.