This paper systematically investigated the expression of S-adenosylmethionine synthetase gene from yeast by using the pET soluble expression system. It was indicated that pET-44a (Nus fusion tag ) as the carrier and Origami (trxB and gor double mutant) as the host were suitable for the soluble expression of the target protein. Furthermore, the same result was obtained when the soluble expression of S-adenosylmethionine synthetase gene from different sources (E. coli, Bacillus subtilis, Bacillus thuringiensiss) were tested. It was also found that the gene from yeast got the highest soluble expression, which the specific activity of SAM synthetase was up to 60.9 U/mg.

Through constructing the plasmid pKD46-Tc and pCP20-Tc which contained tetracycline resistance marker,a Red recombination system in Klebsiella pneumoniae was established.Using the gene wzi,a highly conserved homologous gene of capsule gene,as a target gene,a fragment called △wzi:FK which contained 250 bp homologous segments was constructed and it was transformed into Klebsiella pneumoniae/pKD46-Tc,then resulted six recombinants.The capsule gene wzi was preliminarily verified having been knockout by using the Red recombination system in Klebsiella pneumoniae.