A DNA-BINDING FACTOR (UBF) INTERACTS WITH A POSITIVE REGULATORY ELEMENT IN THE PROMOTERS OF GENES EXPRESSED DURING MEIOSIS AND VEGETATIVE GROWTH IN YEAST

We have studied the bipartite regulatory element UAS(H)/URS1 in the promoter of HOP1, whose product is required for synapsis and correct pairing of homologous chromosomes during the first meiotic division, HOP1 is transcriptionally repressed by the URS1 motif during vegetative growth and induced during meiotic prophase by the UAS(H) motif in cooperation with the bifunctional URS1 site, which is required for full induction of HOPI. While URS1 is bound in vitro by the Buf and Ume6 repressor proteins, we demonstrate for the first time by electrophoretic mobility shift assays and interference footprinting that the UAS(H) site interacts in vitro with a novel factor called UBF (UAS(H) binding factor) which is present in haploid and diploid cycling, as well as sporulating cells, Point mutations in the HOPI UAS(H) motif abolish UBF-dependent DNA binding activity in vitro and meiotic HOP1 gene expression in vivo, Furthermore, we show that UBF binds in vitro to UAS(H)-like sequences in the promoter regions of several meiosis-specific and non-specific genes and propose that UBF mediates gene expression through its interaction with the UAS(H) motif in both cycling and sporulating cells.