2 DISTINCT UPSTREAM REGIONS ARE INVOLVED IN EXPRESSION OF THE CATALASE GENE IN SCHIZOSACCHAROMYCES-POMBE IN RESPONSE TO OXIDATIVE STRESS

The DNA region responsible for the induction of the catalase gene of S chizosaccharomyces pombe in response to oxidative stress was determine d by constructing a series of deletions in the 5'-flanking region of t he gene. Cells having deletion -672 (numbered with the transcription s tart site as +1) to -111 showed no significant difference in catalase expression from the wild-type cells. Cells having deletion -672 to -89 showed reduced basal expression of the catalase mRNA, but retained th e ability of induction in response to oxidative stress. Cells having d eletion -672 to -55 completely lost the ability to express the catalas e mRNA, These results suggested that two regions, -89 to -55 and -111 to -89, are involved in expression of the catalase gene. The DNA regio n of -89 to -55 overlapped with the Atf1 binding sequence. The Atf1 is a bZIP transcription factor with an important role in stress response under the control of the Spc1 mitogen activated protein (MAP) kinase, Introduction of the atf1(-) or spc1(-) mutation into the mutant havin g a deletion in -672 to -89 completely abolished the expression of the catalase mRNA, This result indicated that the Spc1-Atf1 cascade is in volved in expression of the catalase gene through the region of -89 to -55, In mutants spc1(-) and atf1(-), basal expression and induction b y hydrogen peroxide of catalase mRNA were observed. These results reve aled that not only the Atf1 binding site but also another DNA element independent of the Spc1-Atf1 pathway is involved in the expression of the catalase gene in response to oxidative stress in S. pombe. Protein s that bound specifically to each DNA element existed in the cell extr act of the wild-type S. pombe.