The packaging initiation site of phage P22. Analysis of packaging events by transduction

P22 lysates were grown on Salmonella strains carrying P22 prophages deleted to various extents. Transducing bacterial markers at both sides of the prophage insertion site it could be shown that: (i) transduction of markers can be enhanced by the prophage pac site; (ii) the recognition signal pac is in the area of gene 3 on the phage genome and thus close to the cutting site(s); (iii) transposon Tn10 may also act as a signal for packaging initiation; (iv) (at least) Tn10 initiates packaging sequences in both directions.