Identification of New mRNA Targets of Puf3 Protein-Mediated Decay and Analysis of Their Condition-Specific Decay Regulation in Yeast

Eukaryotic Puf proteins function to regulate gene expression by altering mRNA stability. Specifically, Puf proteins bind the 3\u27 untranslated region (UTR) of mRNA targets to stimulate their turnover. Yeast Puf3p was originally found to mediate rapid turnover of COX17 mRNA, which encodes a mitochondrial copper shuttle. More recently, microarray and computational analyses revealed that Puf3p physically associates with \u3e100 nuclear-transcribed mRNAs that encode mitochondrial proteins. Moreover, it was predicted that the steady-state expression levels of these mRNAs are altered by different growth conditions. In this work, I have experimentally validated several new mRNAs that are targeted for turnover by Puf3p, including CYT2 and TUF1. Detailed decay analyses of CYT2 revealed that Puf3p stimulates both deadenylation and decapping of the transcript via 3\u27 UTR binding. I also determined that Puf3p is rapidly activated or inactivated upon carbon source changes. Since Puf3p levels do not decrease under inactivating conditions, Puf3p activity is likely regulated post-translationally