The purpose of this proposal is to systematically and extensively study the determinants and regulation of yeast mRNAs turnover using the power of DNA microarray technology. Because the important parameter, the mRNA half-life, has only been determined for a limited number of individual yeast mRNAs, the first goal of this proposed research is to determine the global profiles of mRNAs half-lives in yeast cells. This goal will be achieved by coupling DNA microarray technique with the established biochemical assays (i.e., inhibition of transcription by thiolutin and by Pol II is mutants). Secondly, to identify new substrates for regulated mRNA decay pathways, the changes in mRNA stability will be determined and analyzed in yeast cells grown under different growth conditions, and upon various environmental stimuli and stresses. Furthermore, known mutants with various RNA turnover defects will be used to investigate the trans- and cis-factors involved in the determination of mRNA stability and how specific cis- or trans-factors act to affect the function of degradative activities. These studies are expected to provide a framework of the regulatory mechanism of eukaryotic mRNA turnover and allow genetic and biochemical expression of a specific gene is regulated and fine-tuned within a cell.