AN EFFICIENT METHOD TO ISOLATE YEAST GENES CAUSING OVEREXPRESSION-MEDIATED GROWTH ARREST

In order to characterize new yeast genes regulating cell proliferation , a number of overexpression-sensitive clones have been isolated from a Saccharomyces cerevisiae cDNA library in a multicopy vector under th e control of the GAL1 promoter, on the basis of growth arrest phenotyp e under galactose-induction conditions. Thirteen of the independent cl ones isolated in this way correspond to previously known genes (predom inantly coding for morphogenesis-related proteins or for multifunction al transcriptional factors), while the remaining 11 independent clones represent new genes with unknown functions. The more stringent condit ions employed in this screening compared with previous ones that also employed a dominant genetics approach to isolate overexpression-sensit ive genes has allowed us to extend the number of yeast genes that exhi bit this phenotype. The effect of overexpression of MCM1 (whose produc t participates in the regulation of a number of apparently unrelated c ellular functions) has been studied in more detail. Galactose-induced overexpression of MCM1 leads to rapid growth arrest at the G(1) or S c ell cycle stages, with many morphologically abnormal cells. Several of the other clones also exhibit a G(1) arrest terminal phenotype when o verexpressed.