Pseudovirulent mutants of lambda b221poriCasnA resulting from mutations in or near oriC, the E. coli origin of DNA replication.

Mutants of the specialized transducing phage lambda b221poriCasnA have been isolated which form plaques on lambda lysogens. Genetic and physical evidence is presented to show that the mutations responsible for the pseudovirulent phenotype map in or near oriC, the origin of chromosomal replication in Escherichia coli.