Use of lacZ fusions to delimit regulatory elements of the inducible divergent GAL1-GAL10 promoter in Saccharomyces cerevisiae.

We present the DNA sequence of a 914-base pair fragment from Saccharomyces cerevisiae that contains the GAL1-GAL10 divergent promoter, 140 base pairs of GAL10 coding sequence, and 87 base pairs of GAL1 coding sequence. From this fragment, we constructed four pairs of GAL1-lacZ and GAL10-lacZ fusions on various types of yeast plasmid vectors. On each type of vector, the fused genes were induced by galactose and repressed by glucose. The response of a GAL1-lacZ fusion to gal4 and gal80 regulatory mutations was similar to the response of intact chromosomal GAL1 and GAL10 genes. A set of deletions that removed various portions of the GAL10 regulatory sequences from a GAL10-CYC1-lacZ fusion was constructed in vitro. These deletions defined a relatively guanine-cytosine-rich region of 45 base pairs that contained sequences necessary for full-strength galactose induction and an adjacent guanine-cytosine rich 55 base pairs that contained sequences sufficient for weak induction.