Sequences upstream of the STE6 gene required for its expression and regulation by the mating type locus in Saccharomyces cerevisiae.

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RESUMO

The STE6 gene of Saccharomyces cerevisiae is an a-specific gene; it is repressed in alpha cells by the alpha 2 product of the mating type locus. To study the role of sequences upstream of STE6 in its regulation and expression, we have determined the DNA sequence of the promoter region, identified the start sites for the STE6 transcript, and identified sequences governing its transcription. Deletions that remove DNA upstream of the STE6 gene were produced and assayed for effects on regulation and expression. The deletions defined two intervals upstream of the STE6 transcription initiation sites. One contains all or part of a negative element; the other contains all or part of a positive element. The negative element is required for repression of STE6 by alpha 2: deletions lacking this element express STE6 constitutively. Such deletions remove a 31-base-pair site, located 135 base pairs upstream of the first transcript start site, that is highly homologous to sites present in the upstream regions of four other genes repressed by alpha 2. These sites are presumably responsible for repression of the a-specific genes by alpha 2. The positive element (a putative upstream activation site) is required for expression of STE6. The deletions define the left boundary of the proposed upstream activation site. Sequence homologies between STE6 and other a-specific genes are found in this region and may mediate activation of this set of genes.

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