Deletion analysis of the Saccharomyces GAL gene cluster : Transcription from three promoters

Abstract

Five deletions, constructed in vitro, have been incorporated into the Saccharomyces Cerevisiae GAL7-GAL10-GAL1 gene cluster on chromosome II. These deletions permit unambiguous assignment of genetic function to each of the previously identified transcribed regions. The GAL7 and GAL10 genes are transcribed right to left while the GAL1 gene is transcribed left to right. A deletion of the divergently transcribed region between GAL10 and GAL1 including the sequences homologous to the 5′ ends of all transcripts for both of these genes results in a GAL7 +, gal10 −, gal1 − genotype. This result suggests that each of these three genes can be transcribed from separate promoter regions. A yeast strain, containing the rna1-1 temperature-sensitive mutation, at non-permissive temperatures accumulates a large RNA containing both GAL7 and GAL10 sequences, a small RNA containing GAL7 sequences and at least three larger RNAs containing GAL1 sequences. Deletion of DNA sequences contained within the larger GAL1 transcripts but beyond the GAL1 (galactokinase) coding sequences results in a strain able to complement gal1 − mutants. This result suggests that the larger transcripts may not be obligate precursors to the stable GAL1 mRNAs.