A STATIONARY-PHASE GENE IN SACCHAROMYCES-CEREVISIAE IS A MEMBER OF A NOVEL, HIGHLY CONSERVED GENE FAMILY

The regulation of cellular growth and proliferation in response to env ironmental cues is critical for development and the maintenance of via bility in all organisms. In unicellular organisms, such as the budding yeast Saccharomyces cerevisiae, growth and proliferation are regulate d by nutrient availability. We have described changes in the pattern o f protein synthesis during the growth of S. cerevisiae cells to statio nary phase (E.K. Fuge, E.L. Braun, and M. Werner-Washburne, J. Bacteri ol. 176:5802-5813, 1994) and noted a protein, which we designated Snz1 p (p35), that shows increased synthesis after entry into stationary ph ase. We report here the identification of the SNZ1 gene, which encodes this protein. We detected increased SNZ1 mRNA accumulation almost 2 d ays after glucose exhaustion, significantly later than that of mRNAs e ncoded by other postexponential genes. SNZ1-related sequences were det ected in phylogenetically diverse organisms by sequence comparisons an d low-stringency hybridization. Multiple SNZ1-related sequences were d etected in some organisms, including S. cerevisiae. Snz1p was found to be among the most evolutionarily conserved proteins currently identif ied, indicating that we have identified a novel, highly conserved prot ein involved in growth arrest in S. cerevisiae. The broad phylogenetic distribution, the regulation of the SNZ1 mRNA and protein in S. cerev isiae, and identification of a Snz protein modified during sporulation in the gram-positive bacterium Bacillus subtilis support the hypothes is that Snz proteins are part of an ancient response that occurs durin g nutrient limitation and growth arrest.