Heat shock factor-independent heat control of transcription of the CTT1 gene encoding the cytosolic catalase T of Saccharomyces cerevisiae

R Wieser,G Adam,A Wagner,C Schüller,G Marchler,H Ruis,Z Krawiec,T Bilinski

doi:10.1016/s0021-9258(18)98912-x

Abstract

Transcription of the Saccharomyces cerevisiae CTT1 gene encoding the cytosolic catalase T has been previously shown to be derepressed by nutrient stress. To investigate whether expression of this gene is also affected by other types of stress, the influence of heat shock on CTT1 expression was studied. The results obtained show that expression of the gene is low at 23 degrees C and is induced rapidly at 37 degrees C. By deletion analysis, a promoter element necessary for high level induction by heat shock was located between base pairs -340 and -364 upstream of the translation start codon. This region was demonstrated to be sufficient for heat shock control by placing it upstream of a S. cerevisiae LEU2-lacZ fusion gene. Mutagenesis of the region showed that the response to heat shock is not mediated by a sequence similar to canonical heat shock elements, but by DNA elements also involved in nutrient control of transcription. Catalase T appears to have a function in protecting yeast cells against oxidative damage under stress conditions. Catalase T-containing strains are less sensitive to exposure to 50 degrees C ("lethal heat shock") than isogenic catalase T-deficient mutants, and catalase T-containing strains pretreated by incubation at 37 degrees C are less sensitive to H2O2 than pretreated catalase-deficient mutants.

Highlights

Transcription of the Saccharomycecserevisiae CTTl gene encoding the cytosolic catalase T has been previously shown to be derepressed by nutrient stress
Expression of the CTTl Gene Is Induced by Heat S h c k To investigate whether the CTTl gene is under control by heat shock, its expression was examined at themRNA level, by assaying the dependence of catalase T activity on heat treatment of cells, and by followingthe expression of a CTTllac2 fusion gene during heat shock
Fig. 1demonstrates that the level of mRNA transcribed from the endogenous CTTl gene is significantly enhanced when yeast cells grown at 23 "C are exposed to a mild heat shock (37 "C)

Summary

RESULTS

Expression of the CTTl Gene Is Induced by Heat S h c k To investigate whether the CTTl gene is under control by heat shock, its expression was examined at themRNA level, by assaying the dependence of catalase T activity on heat treatment of cells, and by followingthe expression of a CTTllac fusion gene during heat shock. Fig. 1demonstrates that the level of mRNA transcribed from the endogenous CTTl gene is significantly enhanced when yeast cells grown at 23 "C are exposed to a mild heat shock (37 "C) In agreement with this observation, 5-10-fold induction of catalase T activity and of @-galactosidaseproduced by expression of a CTTl-lac fusion gene by heat shock is observed (Fig. 2). When corresponding deletions are tested for their effect on heat shock control of a CTTl-lac fusion gene (Table 11), it is evident that all those deletions causing a pronounced decrease in heat shock control (7-10-fold) lack a DNA sequence between base pairs -340 and -364 This region should contain or at least overlap with an element important for heat shock control. To test whether the region containingthe element defined by deletion analysis is sufficient for heat shock control, promoter fragments or synthetic oligonucleo-

Heat Control of Expression of Yeast Catalase Gene

Gene construct

Heat shock element activity ofCTTl upstream fragments

DISCUSSION