We report the detection of a widely distributed Streptomyces strain Y27 and its indige nous plasmid pWTY27 fiom plants and soil samples cross China by both culturing an d nonculturing methods.The complete nucleotide sequence ofpWTY27 consisted of 14,288 bp.A basic locus for plasmid replication comprised repAB genes and an adjacent iteron sequence,to a long inverted-repot of which the RepA protein bound specifically in vitro,suggesting that RepA may recognize a second structure (e.g.a long stem-loop) of the iteron DNA.A plasmid containingthe locus propagated in linear mode when the telomeres of a linear plasmid were attached,indicating a bi-directional replication mode for pWTY27.As for rolling-circle plasmids,a single traA gene and a tnssequence (covering 16 bp within traA and its adjacent 159 bp) on pWTY27 were required for plasrnid transfer.TraA recognized and bound specifically to the two regions of the tns scquencc,one containing all the four DR1 of 7 bp (TGACACC) and one DR2 (CCCGCCC) and most of IR1,and another covering two DR2 and part of IR1,suggesting formation of a high-ordered DNA-protein complex.