title: Functional analysis of hybrid plasmids carrying genes for lambda site-specific recombination.
abstract: A number of hybrid plasmids, carrying lambda genes involved in site-specific integrative recombination, have been constructed in vitro. Analysis of protein synthesis in Escherichia coli minicells has shown that Int protein is synthesized only when int gene is expressed constitutively. The plasmids RSF2124::lambda-CD, RSF2124::lambda-Cint-c57, and pInt lambda were able to integrate into the chromosome of E.coli at the attB. The integration of hybrid plasmids into the genome of bacteria has also been shown for polA1 strains restricting the autonomous replication of ColE1 type plasmids. Genetic markers of hybrid plasmids are maintained in polA1 bacteria for at least 50 generations under nonselective conditions. The Southern blotting experiments using [32P]pBR322 DNA and EcoRI fragments of E. coli polA1 chromosome carrying integrated plasmid pInt lambda demonstrated that in this strain hybrid plasmids can be observed only when integrated into the attB of the chromosome according to Campbell's model of integration. In the cells, where autonomous replication of plasmids is possible, they can be observed both in extrachromosomal and integrated states. The integration of the ColE1 replication origin into the chromosome of bacteria is not lethal for the cells. Only attP and the int gene of lambda are necessary for the integration of hybrid plasmids under conditions of effective int gene expression. If the level of Int protein synthesis is high enough, the prophage excision can be observed in the absence of Xis product. The six-fold decrease of Int protein concentration in the cell (in case of pInt lambda 2 as compared to pInt lambda 1) is critical both for integration and excision.
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics*; D003001:Cloning, Molecular; D004262:DNA Restriction Enzymes / Q000378:metabolism; D004269:DNA, Bacterial; D004274:DNA, Recombinant; D004926:Escherichia coli / Q000235:genetics; D005814:Genes, Viral; D010641:Phenotype; D010957:Plasmids; D011995:Recombination, Genetic
chemical_list: D004269:DNA, Bacterial; D004274:DNA, Recombinant; D004262:DNA Restriction Enzymes