UME6, A NEGATIVE REGULATOR OF MEIOSIS IN SACCHAROMYCES-CEREVISIAE, CONTAINS A C-TERMINAL ZN(2)CYS(6) BINUCLEAR CLUSTER THAT BINDS THE URS1 DNA-SEQUENCE IN A ZINC-DEPENDENT MANNER

UME6 is a protein of 836 amino acids from Saccharomyces cerevisiae that acts as a repressor and activator of several early meiotic genes. UME6 contains, near the C-terminus, the amino acid sequence- C-771-X(2)-C-X(6)-C-X(6)-C-X(2)-C-X(6)-C-, in which the spacings of the six Cys residues are identical to those found in 39 N-terminal Cys-rich DNA binding subdomains of fungal transcription factors. This sequence has been shown in GAL4 and other proteins to form a zinc binuclear cluster. In spite of the different location, the C-rich sequence, cloned and overproduced within the last 111 amino acid residues of UME6, UME6(111), forms a binuclear cluster and exhibits a Zn-dependent binding to the URS1 DNA sequence. The latter, TAGCCGCCGA, is required for the repression or activation of meiosis-specific genes by UME6. UME6(111) contains 1.8 +/- 0.4 mol Zn/mol protein and the Zn can be exchanged for Cd to yield a protein containing 1.9 +/- 0.1 mol Cd/mol protein. At 5 degrees C, (113)Cd(2)UME6(111) shows two Cd-113(2) NMR signals, with chemical shifts of 699 and 689 ppm, similar to those observed for (113)Cd(2)GAL4(149). The magnitude of these chemical shifts suggests that each Cd-113 nucleus is coordinated to four -S- ligands, compatible with a Cd-113(2) cluster structure in which two thiolates form bridging ligands. The entire UME6 gene has been cloned and overexpressed and binds more tightly to the URS1 sequence than the zinc binuclear cluster domain alone. DNase I footprints of UME6 on URS1-containing DNA show that the protein protects the phosphodiesters of the 5'-CCGCCG-3' region within the URS1 sequence.