CTR2 and the nonsense-mediated mRNA decay pathway in Saccharomyces cerevisiae.

The nonsense-mediated mRNA decay (NMD) pathway recognizes and degrades mRNA with premature termination codon and some natural mRNA as well. CTR2 is a natural mRNA degraded by NMD in Saccharomyces cerevisiae. The goals of this research were to identify the sequence features that target the CTR2 mRNA for NMD and the physiological consequences resulting from this degradation. These goals were addressed by making fusion constructs and determining total cellular, cytoplasmic and vacuolar copper levels in wild-type and nmd mutant yeast cells. Features contribute to the NMD-mediated degradation of CTR2 were identified. When cultured in medium with excess copper, nmd mutants accumulated significantly higher vacuolar copper levels than wild-type yeast cells, however nmd mutants accumulated significantly less cytoplasmic copper levels than that in wild-type yeast cells. These results are consistent with the inference that nmd mutants tolerate excess copper as a result of ctr2p transporting excessive copper from cytoplasm into vacuole.