The Saccharomyces cerevisiae Isw2p-Itc1p complex represses INO1 expression and maintains cell morphology.
In the yeast Saccharomyces cerevisiae, IRE1 encodes a bifunctional protein with transmembrane kinase and endoribonuclease activities. HAC1 encodes a transcription factor which has a basic leucine zipper domain. Both gene products play a crucial role in the unfolded protein response. Mutants in which one of these genes is defective also show the inositol-auxotrophic (Ino(-)) phenotype, but the reason for this has not been clear. To investigate the mechanism underlying the Ino(-) phenotype, we screened a multicopy suppressor gene which can suppress the Ino(-) phenotype of the Delta hac1 strain. We obtained a truncated form of the ITC1 gene that has a defect in its 3' region. Although the truncated form of ITC1 clearly suppressed the Ino(-) phenotype of the Delta hac1 strain, the full-length ITC1 had a moderate effect. The gene products of ITC1 and ISW2 are known to constitute a chromatin-remodeling complex (T. Tsukiyama, J. Palmer, C. C. Landel, J. Shiloach, and C. Wu, Genes Dev. 13:686--697, 1999). Surprisingly, the deletion of either ITC1 or ISW2 in the Delta hac1 strain circumvented the inositol requirement and caused derepression of INO1 even under repression conditions, i.e., in inositol-containing medium. These data indicate that the Isw2p-Itc1p complex usually represses INO1 expression and that overexpression of the truncated form of ITC1 functions in a dominant negative manner in INO1 repression. It is conceivable that the repressor function of this complex is regulated by the C-terminal region of Itc1p.
Sugiyama
M
M
Department of Biochemical Engineering and Science, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Iizuka, Fukuoka 820-8502, Japan.
Nikawa
J
J
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D050976:Basic-Leucine Zipper Transcription Factors; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D016153:Genes, Suppressor; D007294:Inositol / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D007296:Myo-Inositol-1-Phosphate Synthase / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D010957:Plasmids; D017510:Protein Folding; D017346:Protein Serine-Threonine Kinases; D012097:Repressor Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors / Q000378:metabolism*
D050976:Basic-Leucine Zipper Transcription Factors; D005656:Fungal Proteins; C091341:HAC1 protein, S cerevisiae; C086468:ISWI protein; D008562:Membrane Glycoproteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D007294:Inositol; C082863:IRE1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D000251:Adenosine Triphosphatases; D007296:Myo-Inositol-1-Phosphate Synthase