Partial replicas of UV-irradiated bacteriophage T4 genomes and their role in multiplicity reactivation.

A physicochemical study was made of the replication and transmission of UV-irradiated T4 genomes. The data presented in this paper justify the following conclusions. (i) For both low and high multiplicity of infection there was abundant replication from UV-irradiated parental templates. It exceeded by far the efficiency predicted by the hypothesis that a single lethal hit completely prevents replication of the killed phage DNA: i.e., some dead phage particles must replicate parts of thier DNA. (ii) Replication of the UV-irradiated DNA was repetitive as shown by density reversal experiments. (iii) Newly synthesized progeny DNA originating from UV-irradiated templates appeared as significantly shorter segments of the genomes than progeny DNA produced from non-UV-irradiated templates. A good correlation existed between the number of UV hits and the number of random cuts that would be needed to reduce replication fragments to the length observed. (iv) The contribution of UV-irradiated parental DNA among progeny phage in multiplicity reactivation was disposed in shorter subunits than was the DNA from unirradiated parental phage. It is important to emphasize that it was mainly in the form of replicative hybrid. These conclusions appear to justify excluding interparental recombination as a prerequisite for multiplicity reactivation. They lead directly to some form of partial replica hypothesis for multiplicity reactivation.