[Plasmid pCQ4 and its phage phiCQ4 of endophytic Streptomyces sp. from Artemisia annua L].

Objective: Large plasmid pCQ4 was detected in Streptomyces sp. W75 from Artemisia annua L. We clonined, sequenced, analyzed and characterized pCQ4.
Methods: Southern hybridization was used to determine restriction map of pCQ4. To clone the full-length of pCQ4, conjugation and recombinational cloning in a BAC vector were used.
Results: The complete nucleotide sequence of pCQ4 consisted of 84833-bp, encoding 129 ORFs which 40 ORFs resembled these of bacterial phages. W75 culture could infect W75 cured of pCQ4 and formed plaques on plate. Phage particle (phiCQ4) was observed by transmission electron microscopy. LinearphiCQ4 DNA was detected on pulsed-field gel electrophoresis. Comparison to Streptomyces plasmid-phage pZL12, genes encoding major phage structural proteins resembled that of pCQ4.
Conclusion: Streptomyces plasmid pCQ4 could be transformed into lytic phagephiCQ4, and the phage segment on pCQ4 might be a mobile unit.