T1 pip: a mutant which affects packaging initiation and processive packaging of T1 DNA

The pip mutation of phage T1 is located between the tar (gene 2.5) and am6 (gene 3) mutations in the region of the T1 genome which codes for early functions. The tar and pip mutations are additive in increasing the efficiency of transduction by T1. When T1 carries the pip mutation the initiation of DNA packaging by the phage at the non-T1, esp-lambda site is more efficient than when the phage is pip+; the small average burst size of 8 to 10 by T1pip suggests that pip causes a reduction in the efficiency with which T1 utilizes pac, the normal packaging initiation site of the phage. The presence of the BglII-D fragment (cut at one end at pac and the other by BglII) after digestion of T1pip DNA by BglII shows that T1pip continues to initiate DNA packaging at pac. The increased molarity of BglII-D coupled with the absence of the BglII-C fragment (which contains DNA on both sides of pac and can only be cut from processively packaged genomes) shows that T1pip packages only genomes which are initiated at pac and is defective in processive packaging.