MET gene expression is driven by large multisubunit complexes which assemble on the 5' upstream regions of the MET genes. These complexes contain Met4p, the single activator required for the transcriptional regulation of the sulfur amino acid pathway, and, depending on the gene, different combinations of the auxiliary factors Met28p, Cbf1p, Met31p, or Met32p (4, 5, 6, 7). Met31p and Met32p are homologous (46% identical) zinc finger-containing proteins, each having an amino-terminal zinc finger of the CC/HH type, and a carboxy-terminal zinc finger of the CC/HC type (1, 8). Met32p, itself devoid of any intrinsic transcription activation function, binds the upstream element 5'-AAACTGTGG-3', which is found in the promoters of some of the methionine biosynthetic genes, and acts in recruiting Met4p to the DNA (1, 8, 9, 6). The function of Met32p during the transcriptional regulation of the sulfur network varies, however, from one gene to another, as it seems to act as a negative trans-regulatory factor at the MET17 promoter region, but as an essential positive effector at the MET3, MET14, and MET30 promoter regions (1, 8, 7). In addition, Met32p is also responsible for regulating GSH1 expression in response to cadmium (9), and may play a role in coregulating genes involved in copper and iron metabolism (10).

Last updated: 2003-05-15