ORGANIZATION OF THE SACCHAROMYCES-CEREVISIAE ACTIN GENE UAS - FUNCTIONAL-SIGNIFICANCE OF REITERATED REB1 BINDING-SITES AND AT-RICH ELEMENTS

The upstream activation sequence (UAS) in the Saccharomyces cerevisiae actin gene promoter contains three different motifs, specifically two AT-rich tracts, two binding sites for the yeast protein REB1, and an Mlul site, Synthetic UAS elements containing individual motifs, or com binations of them, were inserted in place of the natural UAS, and assa yed using a lacZ reporter gene, The REB1 binding sites were found to b e essential for, and sufficient to restore partial, UAS activity, AT-r ich tracts alone were inactive, Multimerization of a REB1 binding site created a UAS that in galactose is more active, but in glucose less a ctive, than a UAS having a single REB1 site with one AT-rich tract, In general, transcription during growth in galactose or glycerol/lactate responds more to multimerization of motifs, The results suggest that the natural actin promoter UAS retains activity on these alternative c arbon sources because of reiteration of sequence elements within it; t he additional elements appear to be redundant when cells are grown on glucose, The Mlul site, which is present upstream of a number of yeast genes involved in DNA synthesis and confers cell cycle periodicity to those genes, contributes to the activity of the synthetic UAS element s, but not in a cell-cycle-dependent manner.