THE YEAST PROTEIN GCR1P BINDS TO THE PGK UAS AND CONTRIBUTES TO THE ACTIVATION OF TRANSCRIPTION OF THE PGK GENE

Analysis of the upstream activation sequence (UAS) of the yeast phosph oglycerate kinase gene (PGK) has demonstrated that a number of sequenc e elements are involved in its activity and two of these sequences are bound by the multifunctional factors Rap1p and Abf1p. In this report we show by in vivo footprinting that the regulatory factor encoded by GCR1binds to two elements in the 3' half of the PGK UAS. These element s contain the sequence CTTCC, which was previously suggested to be imp ortant for the activity of the PGK UAS and has been shown to be able t o bind Gcr1p in vitro. Furthermore, we find that Gcr1p positively infl uences PGK transcription, although it is not responsible for the carbo n source dependent regulation of PGK mRNA synthesis. In order to media te its transcriptional influence we find that Gcr1p requires the Rap1p binding site, in addition to its own, but not the Abf1p site. As neit her a Rap1p nor a Gcr1p binding site alone is able to activate transcr iption, we propose that Gcr1p and Rap1p interact in an interdependent fashion to activate PGK transcription.