Four genes encoding different type I signal peptidases are organized in a cluster in Streptomyces lividans TK21

Four adjacent genes (sipW, sipX, sipY and sipZ) encoding different type I s ignal peptidases, were isolated on a 7860 bp DNA fragment from Streptomyces lividans TK21. Three of the sip genes constitute an operon and the fourth is the first gene of another operon encompassing three additional, unrelate d genes. A DNA fragment containing the four sip genes complemented an Esche richia coil type I signal peptidase mutant when cloned in a multicopy plasm id. Clustering of four different type I signal peptidase genes seems, so fa r, to be a unique feature of Streptomyces.