Genetic evidence for promoter competition in Saccharomyces cerevisiae

The his4-912 delta mutation is an insertion of the long terminal repeat ( delta ) of the yeast retrotransposon Ty into the HIS4 promoter region, such that the delta is 97 base pairs upstream of the HIS4 transcription initiation site. Strains carrying the his4-912 delta allele are His super(-) at 23 degree C; this phenotype can be reversed either by growth at 37 degree C or by mutations in trans-acting SPT) genes. Under conditions in which his4-912 delta confers a His super(-) phenotype, HIS4) transcription initiates at the delta initiation site, rather than at the HIS4 initiation site, producing a longer, nonfunctional transcript. Under conditions in which the strain is His super(+), transcription initiates at the wild-type HIS4) initiation site. To understand how transcription is balanced between the delta and HIS4 promoters, the authors selected for cis-acting suppressors of his4-912 delta .