ABSTRACTThe newly constructed PLtl hybrid promoter is composed of the operator and promoter sequences oftacand the −35 to −135 region of the phage λ PLpromoter, which contains the AT-rich block and the OL2 and OL3 segments. Transcriptional properties of PLtl were examined and compared withtacand λ PLas reference promoters. The hybrid PLtl exhibits different and improved properties overtacpromoter in four ways: (i) when repressed, the repression is almost complete; (ii) after complete induction, the hybrid PLtl promoter shows a 1.4–2 times higher expression; (iii) the hybrid PLtl promoter permits flexible gene expression because it can be utilized under either or both repression controls simultaneously; (iv) the PLtl promoter permits enhanced expression of genes encoding products with unknown properties. When compared with the strong promoter PLfrom phage λ, results with the PLtl promoter inlacZfusion constructs show higher levels of β-galactosidase activity. We also constructed a plasmid vector, pPLtl7G, which contains the hybrid PLtl promoter with a polylinker sequence at its 3′ end, which facilitates efficient fusions of foreign genes in any of the re
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