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Mutation of a phosphorylatable residue in Put3p affects the magnitude of rapamycin-induced PUT1 activation in a Gat1p-dependent manner.
Leverentz MK, Campbell RN, Connolly Y, Whetton A, Reece RJ
J Biol Chem. 2009;.
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Abstract
Saccharomyces cerevisiae can utilise high quality (e.g., glutamine and ammonia) as well as low quality (e.g., gamma-amino butyric acid and proline) nitrogen sources. The transcriptional activator Put3p allows yeast cells to utilise proline as a nitrogen source, through expression of the PUT1 and PUT2 genes. Put3p activates high-level transcription of these genes by binding proline directly. However, Put3p also responds to other lower quality nitrogen sources. As nitrogen quality decreases, Put3p exhibits an increase in phosphorylation concurrent with an increase in PUT gene expression. The proline-independent activation of the PUT genes requires both Put3p and the positively-acting GATA factors, Gln3p and Gat1p. Conversely, the phosphorylation of Put3p is not dependent on GATA factor activity. Here, we find that the phosphorylation of Put3p at amino acid Y788 modulates the proline-independent activation of PUT1 through Gat1p. The phosphorylation of Put3p appears to influence the association of Gat1p but not Gln3p to the PUT1 promoter. Combined, our findings suggest that this may represent a mechanism through which yeast cells rapidly adapt to use proline as a nitrogen source, under nitrogen limiting conditions.