Transcription of two divergently transcribed yeast genes initiates at a common oligo(dA-dT) tract.

Oligo(dA-dT) tracts are frequently found in the intergenic regions of the yeast Saccharomyces cerevisiae and have been proposed to act as upstream promoter elements for constitutive transcription. An oligo(dA-dT) tract of 23 bp is also found as a characteristic sequence motif in the centre of the 230 bp segment which separates the open reading frames of the CBS2 gene and its 5'-flanking gene on chromosome IV. Recently we have reported that transcription of CBS2 is initiated immediately adjacent to this oligo(dA-dT) tract (michaelis et al. 1988). Here we report that the flanking gene of unknown function is divergently transcribed into an RNA with heterogeneous 5' ends. Two of these 5' ends map within the oligo(dA-dT) stretch, while the third is located upstream, leading to an RNA species which is partially complementary to the CBS2 transcript. Gel shift assays show that the oligo(dA-dT) stretch is specifically recognized by (a) binding factor(s) in nuclear extracts. We discuss these results with respect to the role of oligo(dA-dT) stretches in gene expression in yeast.