ROLE OF THE PURINE REPRESSOR HINGE SEQUENCE IN REPRESSOR FUNCTION

A protease-hypersensitive hinge sequence in Escherichia coli purine re pressor (PurR) connects an N-terminal DNA-binding domain with a contig uous corepressor-binding domain. Binding of one molecule of dimeric re pressor to operator DNA protects the hinge against proteolytic cleavag e. Mutations in the hinge region impair repressor function in vivo. Se veral nonfunctional hinge mutants were defective in low-affinity bindi ng to operator DNA in the absence of corepressor as well as in high-af finity corepressor-dependent binding to operator DNA, although binding of corepressor was similar to binding of the wild-type repressor. The se results establish a role for the hinge region in operator binding a nd lead to a proposal for two routes to form the holoPurR-operator com plex.