Function and autoregulation of yeast copperthionein.

The CUP1 gene of yeast encodes a small, metallothionein-like protein that binds to and is inducible by copper. A gene replacement experiment shows that this protein protects cells against copper poisoning but is dispensable for normal cellular growth and development throughout the yeast life cycle. The transcription of CUP1 is negatively autoregulated. This feedback mechanism, which is mediated through upstream control sequences, may play an important role in heavy metal homeostasis.