Isolation and characterization of lambda b221poriCasnA, a plaque-forming specialized transducing phage carrying the origin of replication of the Escherichia coli chromosome.

A specialized transducing phage lambda b221poriCasnA has been isolated carrying oriC the origin of chromosomal replication of Escherichia coli. All phage genes required for lytic growth are retained, thus the phage is capable of lytic growth. The presence of the oriC locus confers upon infecting phage DNA the ability to replicate as a plasmid using only host DNA replication functions. The presence of both oriC and ansA markers has allowed the development of a plaque assay for origin function which can be used to identify mutants at these loci. Comparison of restriction endonuclease cleavage sites present on lambda b221proiCasnA DNA to those on its parent, lambda b221 rex::Tn10 suggests the steps involved in the formation of the transducing phage.