Transcriptional regulation of the one‐carbon metabolism regulon in Saccharomyces cerevisiae by Bas1p

Abstract

SummaryThe mechanisms mediating responses to glycine withdrawal in budding yeast were studied using a genome-wide profiling approach. A striking pattern of repressed expression of genes with an enrichment for those involved in one-carbon metabolism and AMP biosynthesis was revealed. Sequence analysis of the promoters for the most severely repressed genes identified a conserved sequence, TGACTC, a known binding site for the transcription factors Gcn4p and Bas1p. Loss of BAS1 abolished or significantly reduced the repression of these genes in response to glycine removal but this phenotype was much less apparent in the absence of BAS2 or GCN4 . Addition of a Bas1p-LexA fusion protein to a strain with a LexAop-LacZ fusion showed a strong glycine effect both in a BAS2 and a bas2 background. A Bas1p-VP16 fusion protein activated expression in a bas1bas2 strain but no glycine effect was observed while a Bas1p-Bas2p fusion protein activated expression to a lesser extent with a slight stimulation by glycine. These results suggest that glycine affects Bas1p activation of transcription rather than DNA binding and that Bas2p is not required for this affect. Glycine withdrawal repressed many of the same genes as addition of adenine, a process known to be dependent on Bas1p. However, the glycine response is independent of adenine repression, because glycine regulation occurs normally in ade strains. We did not see any difference in the degree of stimulation by glycine in the presence or absence of adenine even in Ade + strains. Glycine regulation was also found to be dependent on an intact SHM2 gene, which encodes cytoplasmic serine hydroxymethyltransferase. A reporter plasmid containing a DNA sequence from the GCV2 promoter which confers glycine regulation on heterologous genes was introduced into the yeast deletion set to screen for genes required for glycine regulation. A number of genes, including BAS1 were required for activation by glycine but only the SHM2 gene was required for repression in the absence of glycine. We also showed that regulation of the SHM2 promoter by glycine requires Bas1p but not Bas2p or Gcn4p using a b b b b -galactosidase reporter. The response of the promoter to glycine required an intact SHM2 gene but was restored in a shm2 strain by addition of formate to the medium.

A Genetic Screen for Increased Loss of Heterozygosity inSaccharomyces cerevisiae

“…Full induction of RNR activity requires Dun1, and in a parallel pathway, Pop2 and Ccr4 (components of the Ccr4-Not complex) (Huang et al 1998;Zhao and Rothstein 2002;Mulder et al 2005;Woolstencroft et al 2006). In addition, there are several links between glycine metabolism and de novo purine biosynthesis (Subramanian et al 2005;Christensen and Mackenzie 2006). Consistent with this, gly1D mutants are HU sensitive and have reduced dNTP pools (Hartman 2007).…”

Systems-Level Engineering of Nonfermentative Metabolism in Yeast

“…Under conditions of glycine induction Gelling et al (2004) noticed a similar pattern of C1 enzyme differential expression; however, Bas1 was not required for the observed effect in this case. In both of these studies the intact cytosolic serine hydroxymethyltransferase Shm2 (EC 2.1.2.1) was necessary for glycine-dependent changes in C1 enzyme expression (Gelling et al 2004;Subramanian et al 2005). Although contradicting evidence exists, results reported thus far demonstrate the dynamic control of C1 metabolism in eukaryotes.…”

“…Two groups have independently shown that C1 enzymes are controlled dynamically by glycine at the transcriptional level. Upon glycine withdrawal many enzymes involved in C1 metabolism are strongly repressed, a regulatory event that requires the transcription factor Bas1 (Subramanian et al 2005). Under conditions of glycine induction Gelling et al (2004) noticed a similar pattern of C1 enzyme differential expression; however, Bas1 was not required for the observed effect in this case.…”

Life in the midst of scarcity: adaptations to nutrient availability in Saccharomyces cerevisiae

“…The proteins that control phosphorylation of Pho2 under physiological conditions have not been identified, but it is known that the Cdc28 is able to phosphorylate Pho2 in vitro (Liu et al 2000). Note that the function of Pho2 is not restricted to phosphate signalling, as this cofactor is also involved in mating-type switching, through its interaction with Swi5 (Bhoite and Stillman 1998;Bhoite et al 2002), as well as in one-carbon metabolism and especially adenine synthesis, through interaction with Bas1 (Zhang et al 1997;Bhoite et al 2002;Subramanian et al 2005). The latter is of particular interest since it provides a link between phosphate signalling and adenylic nucleotide synthesis as will be discussed below.…”