TRANSFER-FUNCTIONS OF THE CONJUGATIVE INTEGRATING ELEMENT PSAM2 FROM STREPTOMYCES-AMBOFACIENS - CHARACTERIZATION OF A KIL-KOR SYSTEM ASSOCIATED WITH TRANSFER

pSAM2 is an 11-kb integrating element from Streptomyces ambofaciens. D uring matings, pSAM2 can be transferred at high frequency, forming poc ks, which are zones of growth inhibition of the recipient strain. The nucleotide sequences of the regions involved in pSAM2 transfer, pock f ormation, and maintenance have been determined. Seven putative open re ading frames with the codon usage typical of Streptomyces genes have b een identified: traSA (306 amino acids [aa]), orf84 (84 aa), spdA (224 aa), spdb (58 aa), spdC (51 aa), spdD (104 aa), and korSA (259 aa). t raSA is essential for pSAM2 intermycelial transfer and pock formation. It could encode a protein with similarities to the major transfer pro tein, Tra, of pIJ101. TraSA protein contains a possible nucleotide-bin ding sequence and a transmembrane segment. spdA, spdB, spdC, and spdD influence pock size and transfer efficiency and may be required for in tramycelial transfer. A kil-kor system similar to that of pIJ101 is as sociated with pSAM2 transfer: the korSA (kil-override) gene product co uld control the expression of the traSA gene, which has lethal effects when unregulated (Kil phenotype). The KorSA protein resembles KorA of pIJ101 and repressor proteins belonging to the GntR family. Thus, the integrating element pSAM2 possesses for transfer general features of nonintegrating Streptomyces plasmids: different genes are involved in the different steps of the intermycelial and intramycelial transfer, a nd a kil-kor system is associated with transfer. However, some differe nces in the functional properties, organization, and sizes of the tran sfer genes compared with those of other Streptomyces plasmids have bee n found.