Transcriptional regulation of the yeast DnaJ homologue SIS1

The Saccharomyces cerevisiae SIS1 gene encodes an essential heat shock protein with similarity to the Escherichia coli DnaJ protein. In sis1-85 and sis1-86 mutants, the sis1 RNA is induced to high levels at room temperature and without heat shock. The presence of wild type SIS1 in the sis1-85 mutant represses the overexpression of SIS1-85 protein. Furthermore, overexpression of wild type SIS1 reduces the β-galactosidase activity expressed from a SIS1:lacZ fusion. These results suggest that SIS1 negatively regulates its own expression. The autoregulation of SIS1 transcription is mediated through a 39-base pair cis-element containing the SIS1 heat shock element plus additional flanking sequences on one side. Although SIS1 transcription is constitutive, it is transiently induced upon heat shock. In addition, SIS1 transcription is regulated by SSA (a class of HSP70 proteins) function. The elevated transcription of SIS1 in ssa1 ssa2 mutants is mediated solely through the SIS1 heat shock element. Therefore, the SIS1 autoregulatory element is different from the SSA-responsive element, suggesting that the mechanism involved in autoregulation of SIS1 is distinct from regulation of SIS1 by SSA proteins.