IDENTIFICATION OF STREPTOMYCES-VIOLACEORUBER TU22 GENES INVOLVED IN THE BIOSYNTHESIS OF GRANATICIN

A 50 kb region of DNA from Streptomyces violaceoruber Tu22, containing genes encoding proteins involved in the biosynthesis of granaticin, w as isolated. The DNA sequence of a 7.3 kb fragment from this region, l ocated approximately 10 kb from the genes that encode the polyketide s ynthetase responsible for formation of the benzoisochromane quinone sk eleton, revealed five open reading frames (ORF1-ORF5). The deduced ami no acid sequence of GraE, encoded by ORF2, shows 60.8% identity (75.2% similarity) to a dTDP-glucose dehydratase (StrE) from Streptomyces gr iseus. Cultures of Escherichia coli containing plasmids with ORF2, on a 2.1 kb BamHI fragment, were able to catalyze the formation of dTDP-4 -keto-6-deoxy-D-glucose from dTDP-glucose at 5 times the rate of contr ol cultures, confirming that ORF2 encodes a dTDP-glucose dehydratase. The amino acid sequence encoded by ORF3 (GraD) is 51.4% identical (69. 9% similar) to that of StrD, a dTDP-glucose synthase from Streptomyces griseus. The amino acid sequence encoded by ORF4 shares similarities with proteins that confer resistance to tetracycline and methylenomyci n, and is suggested to be involved in transporting granaticin out of t he cells by an active efflux mechanism.