The emerging regulatory potential of SCF(Met30 )-mediated polyubiquitination and proteolysis of the Met4 transcriptional activator

The yeast SCF(Met30 )ubiquitin ligase plays a critical role in cell division by regulating the Met4 transcriptional activator of genes that control the uptake and assimilation of sulfur into methionine and S-adenosyl-methionine. The initial view on how SCF(Met30 )performs its function has been driven by the assumption that SCF(Met30 )acts exclusively as Met4 inhibitor when high levels of methionine drive an accumulation of cysteine. We revisit this model in light of the growing evidence that SCF(Met30 )can also activate Met4. The notion that Met4 can be inhibited or activated depending on the sulfur metabolite context is not new, but for the first time both aspects have been linked to SCF(Met30), creating an interesting regulatory paradigm in which polyubiquitination and proteolysis of a single transcriptional activator can play different roles depending on context. We discuss the emerging molecular basis and the implications of this new regulatory phenomenon.