Defective Phage Formation by Lysogens of Integration

Integration deficient (L) mutants of phage P22 can be complemented with L+ phage to yield L mutant lysogens. Once established the L prophage is stable in the absence of L+ function. Ultraviolet or thermal induction of L lysogens leads to product,ion of defective phage particles and low yields of infectious phage. The defective particles contain a normal amount of DNA but the DNA is mainly bacterial in origin and appears to derive from the pro C region adjacent to one end of the prophage. The defective lysates t,ransduce pro C at high frequency relative to other bacterial markers. The representation of phage genes is strongly polar with markers distal to pro C being rarely present. It appears that L+function is required not only for efficient integration of the prophage, but for normal recovery of the prophage genome following induction.