DATIN, A YEAST POLY(DA-DT)-BINDING PROTEIN, BEHAVES AS AN ACTIVATOR OF THE WILD-TYPE ILV1 PROMOTER AND INTERACTS SYNERGISTICALLY WITH REB1P

A cis-acting element required for GCN4-independent basal-level transcr iption of ILV1 was previously identified in our laboratories as a bind ing site for the REB1 protein (Reb1p). Further deletion analysis of th e ILV1 promoter region identified a second element also required for G CN4-independent basal-level ILV1 expression. This second element is an A.T-rich tract (26 As out of 32 nucleotides) situated 15 bp downstrea m of the Reb1p-binding site. Deletion of both the Reb1p site and the p oly(dA:dT) element totally eliminates basal activity of the ILV1 promo ter. We show that the two elements act synergistically to control ILV1 expression and that the synergistic effect is distance dependent. We demonstrate that (i) datin (Dat1p), the only known poly (dA:dT)-bindin g protein in yeast, specifically binds to the ILV1 poly(dA:dT) element in vitro; (ii) Dat1p functions as a trans-activating factor in the IL V1 context; and (iii) the synergistic activation observed in vivo betw een the Reb1p site and the poly(dA:dT) element depends on the presence of the structural gene for Dat1p, DAT1.