Saccharomyces cerevisiae gene ISW2 encodes a microtubule-interacting protein required for premeiotic DNA replication

A molecular genetic characterization of the ORF YOR304W (ISW2), identified in a screen of a yeast lambda gt11 library using a monoclonal antibody that reacts with a 210 kDa mammalian microtubule-interacting protein, is presen ted in this paper. The protein encoded by the ORF YOR304W is 50% identical to the Drosophila nucleosome remodelling factor ISWI and is therefore a new member of the SNF2 protein family and has been recently entered into SDG a s ISW2. Although not essential for vegetative growth, we found that the ISW 2 gene is required for early stages in sporulation. The isw2 homozygous del etant diploid strain was blocked in the G(1) phase of the cell cycle, unabl e to execute the premeiotic DNA replication and progress through the nuclea r meiotic division cycle. ISW2 expression from a multicopy plasmid had the same effect as deletion, but ISW2 expression from a centromeric plasmid res cued the deletion phenotype. In vegetatively growing diploid cells, the Isw 2 protein was preferentially found in the cytoplasm, co-localizing with mic rotubules. An accumulation of the Isw2 protein within the nucleus was obser ved in cells entering sporulation. Together with data published very recent ly by Tsukiyama et al. (1999), we propose a role for the Isw2 protein in fa cilitating chromatin accessibility for transcriptional factor(s) that posit ively regulate meiosis/sporulation-specific genes. Copyright (C) 2000 John Wiley & Sons, Ltd.