A cosmid (pPR1347) carrying both the rfb gene cluster and the rfc gene
of a Salmonella group B serovar has been constructed; Escherichia col
i K-12 strains carrying this cosmid produce long-chain O antigen, are
sensitive to phage P22, and can be transduced by P22. Some of the bene
fits of P22 transduction are now available for studying E. coli and po
tentially other genera.