Selection of lambda Spi − transducing phages using the P2 old gene cloned onto a plasmid

Abstract

The old gene product of the P2 prophage interferes with plaque formation by λ wild type phage but allows λ phages whose red and gam genes have been deleted to form small, visible plaques (the λ Spi − phenotype). The old gene product also kills Escherichia coli recB or recC mutants. We have cloned the old gene into the high-copy-number plasmid pBR322, where it prevents plaque formation by both λSpi + and λASpi − phages. We transferred a DNA fragment that carries the old gene to the low-copy-number plasmid pSClOl and found that λSpi − phages can be selected on strains that carry this plasmid. The plasmid-bome old gene kills E. coli recB mutants, providing a selection for old − mutants.