The product of the SNF2/SWI2 paralogue INO80 of Saccharomyces cerevisiae required for efficient expression of various yeast structural genes is part of a high-molecular-weight protein complex

Structural genes of phospholipid biosynthesis in the yeast Saccharomyces ce revisiae are activated by the Ino2p/Ino4p transcription factor that binds t o ICRE promoter motifs and mediates maximal gene expression in the absence of inositol. We identified the ino80 mutation causing inositol auxotrophy a s a result of a defect in ICRE-dependent gene activation. The product of th e corresponding wild-type gene INO80 (= YGL150C) shows significant similari ty to the Snf2p family of DNA-dependent ATPases, Nevertheless, SNF2 in incr eased gene dosage did not suppress ino80 mutant phenotypes, Mutation of the Ino80p lysine residue corresponding to the NTP binding site of Snf2p led t o a non-functional protein, In ino80 null mutants, gene activation mediated by an ICRE decreased to 16% of the wild-type level, Maximal expression of PHO5, GAL1, CYC1 and ICL1 was also significantly reduced, Thus, Ino80p affe cts several transcription factors involved in unrelated pathways, As demons trated by gel filtration, Ino80p is part of a high-molecular-weight complex of more than 1 MDa. Similar to what was found for Snf2p, the Ino80p-contai ning complex may influence the transcriptional level of several unrelated s tructural genes by functioning as an ATPase that possibly acts on chromatin .