Construction of Recombinant Plasmid pSJM3 Containing par Region and Study on Its Stability
含par位点的重组质粒Psjm3的构建及其稳定性研究

The plasmids pSJM4 and pSJM3,which contain both par region,were constructed.The comparative studies on stabilities of plasmids in same host ( E.coli HB101) showed that recombinant plasmid pSJ3 containing 2 8kb alkakine protease gente fragment but not par region was very instable.Some of G3(pSJ3) strains lost their plasmids when they were cultured to 10 generations in nonselected medium,and no plasmids,essentially,were detected to 50 generations.However,the recombinant plasmid pSJM3 which consists of pSJ3 and par region was extremly stable.When G3 1(pSJM3) strain was cultured even to 70 generations,no plasmids were almost lost from their host populations,and rate of stability is over 97%.Same result was obtained by comparative studies on stabilities between pUC18(par) and pSJM4 (par ) The comparison of activities of alkaline protease produced by strains G3 (pSJ3) and G3 1(pSJM3) indicated that the enzyme activity produced by strain G3 1(pSJM3) was higher than that of strain G3 (pSJ3).It is proved that function of par region inserted in pSJM3 not only is unaffected by expression of foreign genes but is favourable