TRANSFER OF THE PLJ101 PLASMID IN STREPTOMYCES-LIVIDANS REQUIRES A CIS-ACTING FUNCTION DISPENSABLE FOR CHROMOSOMAL GENE-TRANSFER

The tra gene of Streptomyces lividans plasmid pIJ101 is required for both plasmid DNA transfer and pIJ101-induced mobilization of chromasomal genes during mating. We show that a chromosomally inserted copy of tra mediates transfer of chromosomal DNA at high frequency but promotes efficient transfer of plasmids only when they contain a previously unknown locus, here named clt. Insertional mutation or deletion of clt from plJ101 reduced plasmid transfer mediated by either plasmid-borne or chromosomally located tra by at least three orders of magnitude, abolished the transfer-associated pecking phenomenon, and interfered with the ability of tra(+) plasmids to promote transfer of chromosomal DNA. Our results indicate that plasmid transfer in S. lividans involves a cis acting function dispensable for chromosomal gene transfer and imply that either the S. lividans chromosome encodes its own clt-like function or, alternatively, that transfer of plasmid and chromosomal DNA occurs by different mechanisms.