Résumé
In the yeast, environmental challenges are known to induce both specific and general stress response. The HSP30 gene is strongly induced when cells are exposed to various stresses but this activation is largely independent of the major stress-related transcription factor Hsf1p and partly independent from Msn2p/Msn4p. In order to identify new potential regulators of HSP30 we isolated insertion mutants affected in HSP30 expression. We identified SFL1 gene encoding a protein previously shown to repress several genes. We show that Sfl1 is involved in the transcriptional activation of HSP30. Mutation of sfl1 reduces HSP30-lacZ expression under both basal and stress-induced conditions. We also show, using site-directed mutagenesis, that HSL motifs (Heat-Shock-Like putative DNA binding sequence) located in HSP30 promoter are required for HSP30 activation. Finally, a genome-wide analysis of the effects of SFL1 deletion on gene expression revealed that Sfl1p controls the expression of a small number of genes, with some being activated by the protein and others repressed. As a whole our data show that Sfl1p is a key component of the transcriptional control of the stress responsive gene HSP30. Moreover, we show that Sfl1, which was previously described as being a transcriptional repressor, can also act as an activator.