Transcriptional Regulation of theSMK1Mitogen-Activated Protein Kinase Gene during Meiotic Development inSaccharomyces cerevisiae

Abstract

Meiotic development (sporulation) in Saccharomyces cerevisiae is characterized by an ordered pattern of gene expression, with sporulation-specific genes classified as early, middle, mid-late, or late depending on when they are expressed. SMK1 encodes a mitogen-activated protein kinase required for spore morphogenesis that is expressed as a middle sporulation-specific gene. Here, we identify the cis-acting DNA elements that regulate SMK1 transcription and characterize the phenotypes of mutants with altered expression patterns. The SMK1 promoter contains an upstream activating sequence (UAS S ) that specifically interacts with the transcriptional activator Abf1p. The Abf1p-binding sites from the early HOP1 and the middle SMK1 promoters are functionally interchangeable, demonstrating that these elements do not play a direct role in their differential transcriptional timing. Timing of SMK1 expression is determined by another cis-acting DNA sequence termed MSE (for middle sporulation element). The MSE is required not only for activation of SMK1 transcription during middle sporulation but also for its repression during vegetative growth and early meiosis. In addition, the SMK1 MSE can repress vegetative expression in the context of the HOP1 promoter and convert HOP1 from an early to a middle gene. SMK1 function is not contingent on its tight transcriptional regulation as a middle sporulationspecific gene. However, promoter mutants with different quantitative defects in SMK1 transcript levels during middle sporulation show distinct sporulation phenotypes.The life cycle of the yeast Saccharomyces cerevisiae comprises a series of interconnected growth states and developmental programs that are under both genetic and environmental control. Meiotic development (sporulation) is induced when a diploid cell is starved for essential nutrients and a fermentable carbon source (21). Following induction, the cell withdraws from the mitotic cycle at G 1 and enters meiotic prophase, during which a single round of DNA replication, synaptonemal complex formation, and recombination occur. Meiotic prophase is followed by the meiosis I reductional and meiosis II equational divisions. Spore wall morphogenesis initiates with the outgrowth of a double membranous structure (the prospore wall) from the outer plaques of each meiosis II spindle pole body which envelops each haploid meiotic product. Two layers that appear similar to the vegetative cell wall and two protective spore-specific layers are subsequently assembled from within and around the prospore wall. The end product of sporulation is the differentiated ascus which contains four dormant haploid spores. The tightly regulated sequence of cell cycle and morphogenetic events that occur during sporulation provides a model system for study of the mechanisms that regulate and coordinate development.During sporulation, specific sets of genes that can be classified as early, middle, mid-late, or late are sequentially expressed. Early genes are expressed at the onset of sporulation and are i...

The Ras/cAMP Pathway and the CDK-Like Kinase Ime2 Regulate the MAPK Smk1 and Spore Morphogenesis in Saccharomyces cerevisiae

“…Ime2 positively regulates Ndt80 (Sopko et al 2002;Benjamin et al 2003) and Ndt80 activates the expression of Ama1 and Ssp2, which function in the Smk1 pathway McDonald et al 2005). Ndt80 also activates the expression of Cak1, the only known protein that is required for all detectable phosphorylation of Smk1 (Schaber et al 2002) and Smk1 itself (Pierce et al 1998). Thus, it is likely that Ime2 can promote activation of the Smk1 pathway through Ndt80.…”

Sporulation in the Budding Yeast Saccharomyces cerevisiae

“…The requirement for Ime2, an Ime1/Ume6-induced gene, means that the induction of NDT80 occurs after the broader induction of early genes and it is therefore referred to as a pre-middle gene (Hepworth et al 1998). A few other genes with similar early-middle timing have been reported and, in at least one instance, the SMK1 gene, it appears that a combination of URS1 and MSE elements may regulate expression (Hepworth et al 1998;Pierce et al 1998).…”

Arg-Pro-X-Ser/Thr Is a Consensus Phosphoacceptor Sequence for the Meiosis-Specific Ime2 Protein Kinase in Saccharomyces cerevisiae

“…Some MSGs, however, including NDT80 itself, have a second layer of control to ensure they are not expressed inappropriately. Genes in this subset of MSGs have MSEs that are recognized by Ndt80 during meiosis, but are also bound by the transcriptional repressor Sum1 during mitosis and early meiosis (18,19,33). Sum1 is transiently destabilized during meiosis, and Sum1 repression is removed during late prophase (13).…”