Rsp5-Bul1/2 complex is necessary for the HSE-mediated gene expression in budding yeast

Rsp5 is an essential ubiquitin ligase in Saccharomyces cerevisiae and is concerned with many functions such as endocytosis and transcription through ubiquitination of various substrates. Bul1 or its homologue Bul2 binds to Rsp5 through the PY-motif and the bul1 bul2 double mutant is sensitive to various stresses. We demonstrate here that heat shock element (HSE)-mediated gene expression was defective in both rsp5-101 and bul1 bul2 mutants under high temperature condition. The bul1 gene containing mutations in the PY motif region did not recover this defective gene expression of the bul1 bul2 mutant. The protein level and phosphorylation state of the HSE-binding transcription factor, Hsf1, was not affected by these mutations. Thus, the Rsp5-Bul1/2 complex has a new function for the HSE-mediated gene expression and may regulate it through other factors than Hsf1.