THE ASPERGILLUS-NIDULANS SULFUR REGULATORY GENE SCONB ENCODES A PROTEIN WITH WD40 REPEATS AND AN F-BOX

The Aspergillus nidulans gene sconB, one of the four identified genes controlling sulphur metabolite repression, was cloned and analysed. It encodes a polypeptide of 678 amino acids containing seven WD repeats characteristic of the large WD40 family of eukaryotic regulatory prote ins. The SCONB protein has nuclear localisation signals and is very si milar to the Neurospora crassa SCON2 and Saccharomyces cerevisiae Met3 0 proteins, both of which are involved in the regulation of sulphur me tabolism. The N. crassa scon-2 gene complements the sconB2 mutation. A ll three proteins also contain a newly identified motif, the F-box, fo und in a number of eukaryotic regulatory proteins. This motif is respo nsible, at least in some cases, for ubiquitin-mediated proteolysis. Th e sconB transcript is derepressed under sulphur limitation conditions and partly repressed by high methionine.