Late gene mutants of bacteriophage λ as an efficient expression vector

The disadvantage of a bacteriophage λ expression system is that the replicated λ DNA containing a foreign gene is coated by a phage head, and cell lysis occurs before sufficient expression of the cloned gene. The late genes of the bacteriophage λ system are related to λ DNA packaging and host cell lysis. This study investigated the late gene mutants of the bacteriophage λ in an attempt to develop an efficient expression vector system. The bacteriophage λNM1070, which is a W−, E− and S− mutant, had increased cell longevity due to the S− mutation. However, the genetic stability of this expression system was not high enough because the W− and E− mutation caused a defect in its re-infection. The bacteriophage λHL1, which is a Q− mutant, represses the transcription of all the late genes, even though this repression was not complete. This incomplete repression was rather beneficial to the cloned gene expression because it produced some matured phage particles, which re-infected the segregated host cell and increased the genetic stability. Therefore, a double mutant of the genes S and Q was constructed in order to exploit the merits of λNM1070 and λHL1. This λQ−S− mutant had higher host cell longevity and cloned gene expression than the λNM1070 and λHL1.