Replication and conjugation of Streptomyces small plasmid pDYM4. 3k
链霉菌小质粒pDYM4.3k的复制与接合转移

Objective] Streptomyces sp.X335,harboring a 4.3-kb plasmid pDYM4.3k,was isolated from Tibet sample.Cloning,sequencing,analyzing and functional investigations of pDYM4.3k.Methods] Prime walking to obtain plasmid sequence,BLAST to predict gene function,Southern hybridization to determine replication intermediates,and mating to test conjugal function of plasmid.Results] The complete nucleotide sequence of pDYM4.3k consisted of 4346 bp,encoding 3 genes of which one resembled Streptomyces major conjugative gene tra and other two were with unknown functions.Experiments demonstrated that a new gene of pDYM4.3k and its upstream c.300 bp were required for plasmid replication.Single-stranded pDYM4.3k as a replication intermediate was detected,indicating it rolling-cirle replication mode.pDYM4.3k could conjugal transfer among Streptomyces lividans.Conclusion] Streptomyces small plasmid pDYM4.3k was able to autonomous replication and conjugal transferring.