Abstract
pSN22, an 11 kb multicopy conjugative plasmid from Streptomyces nigrifaciens, promotes chromosome recombination in Streptomyces lividans. Five genes have been identified to be involved in plasmid transfer and pock formation: traB is essential for plasmid transfer; traA for pock formation; spdA and spdB are concerned with pock size; and traR, which corresponds to a kor gene in a kil-kor system, encodes a repressor of traR itself and the traA-traB-spdB (tra) operon. Studies on the interaction of TraR with promoter regions suggest that the negative regulation of transfer-related genes by TraR is achieved by two mechanisms, i.e. promoter hiding and roadblock. The predicted ATPase activity and the membrane localization of TraB suggest that the protein plays a direct role in ATP-driven DNA translocation. TraB is also thought to be involved in intra- and intermycelial transfers of pSN22.
