Two tandem promoters to increase gene expression in Lactococcus lactis

Two plasmids, pPAH and pAH, containing a staphylokinase variant gene (sakXH) under the control of two tandem promoters (P₃₂-P_lacA) or promoter P_lacA alone were constructed and introduced into Lactococcus lactis MG5267. The expression of sakXH in the strain MG5267(pPAH) was approximately twice as high as that in the strain MG5267(pAH), according to the formation of fibrinolytic halos on fibrinolytic plates detected at the same conditions, indicating that the two tandem promoters were stronger than one alone. Difference between the expressions of sakXH under the inducible and non-inducible conditions suggested that P_lacA retained its feature as an inducible promoter when fused to promoter P₃₂.