Identification of cis and trans components of a novel heat shock stress regulatory pathway in Saccharomyces cerevisiae.

The stress-responsive DDR2 gene (previously called DDRA2) of Saccharomyces cerevisiae is transcribed at elevated levels following stress caused by heat shock or DNA damage. Previously, we identified a 51-bp promoter fragment, oligo31/32, which conferred heat shock inducibility on the heterologous CYC1-lacZ reporter gene in S. cerevisiae (N. Kobayashi and K. McEntee, Proc. Natl. Acad. Sci. USA 87:6550-6554, 1990). Using a series of synthetic oligonucleotides, we have identified a pentanucleotide, CCCCT (C4T), as an essential component of this stress response sequence. This element is not a binding site for the well-characterized heat shock transcription factor which recognizes a distinct cis-acting heat shock element in the promoters of many heat shock genes. Here we demonstrate the ability of oligonucleotides containing the C4T sequence to confer heat shock inducibility on the reporter gene and show that the presence of two such elements produces more than additive effects on induction. Gel retardation experiments have been used to demonstrate specific complex formation between C4T-containing fragments and one or more yeast proteins. Formation of these complexes was not competed by fragments containing mutations in the C4T sequence nor by heat shock element-containing competitor DNAs. Fragments containing the C4T element bound to a single 140-kDa polypeptide, distinct from heat shock transcription factors in yeast crude extracts. These experiments identify key cis- and trans-acting components of a novel heat shock stress response pathway in S. cerevisiae.