Transfer of the plJ101 plasmid in Streptomyces lividans requires a cis‐acting function dispensable for chromosomal gene transfer

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Abstract
Summary: The tra gene of Streptomyces lividans plasmid plJ101 is required for both plasmid DNA transfer and plJ101‐induced mobilization of chromosomal 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 pocking 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.