Isolation and characterization of temperature-sensitiveplc1 mutants of the yeastSaccharomyces cerevisiae

ThePLC1 gene of the yeastSaccharomyces cerevisiae has been discovered to encode a homolog of mammalian phosphoinositide-specific phospholipase C (PLC). Five temperature-sensitiveplc1 mutants were isolated by in vitro mutagenesis with subsequent plasmid shuffling. All of the amino acid substitutions that caused a temperature-sensitive growth phenotype were located in the X or the Y region, both of which are conserved among PLC isoenzymes. The PLC activity of all products of mutantplc1 genes was dramatically lower than that of the wild-type product, indicating that PLC activity itself is important for cell growth. At the restrictive temperature,plc1 mutant cells ceased growth at random times during the cell cycle, a result that suggests thatPLC1 is required at several or all stages of the cell cycle.