EXPRESSION ANALYSIS OF THE SSGA GENE-PRODUCT, ASSOCIATED WITH SPORULATION AND CELL-DIVISION IN STREPTOMYCES-GRISEUS

The ssgA gene of Streptomyces griseus B2682, when present in high copy number, results in both suppression of sporulation and fragmented gro wth of mycelia. Western analysis with polyclonal antibodies against th e gene product (SsgA) revealed a close correlation between SsgA accumu lation and the onset of sporulation in wild-type cells. The protein wa s only detected in the cytoplasm. Certain developmental mutants of S. griseus (afs, relC and brgA) which are defective in aerial mycelium fo rmation in solid culture and submerged spore formation in liquid cultu re failed to accumulate SsgA. The SsgA protein appeared shortly (1 h) after nutritional shift-down of strain B2682 cells. afs mutant cells s porulated and expressed SsgA only when A-factor was present both befor e and after nutritional shift-down. Introduction of the ssgA gene in a low-copy-number vector into strain B2682 resulted in fivefold overexp ression of SsgA, and was accompanied by fragmented growth of mycelia a nd suppression of submerged spore formation (in liquid culture) and ae rial mycelium formation (in solid culture). Streptomycin production wa s not inhibited. In a control experiment, a nonfunctional ssgA gene po ssessing a frameshift mutation near its N-terminus had no effect on ei ther growth or sporulation. It is proposed that the ssgA gene product plays a role in promoting the developmental process of S. griseus.