Formation In Vitro of Infective Joint Molecules of λ DNA by T4 Gene-32 Protein

Half molecules of λ DNA that had been partially digested by λ exonuclease to expose homologous single strands were rejoined by the action of T4 gene-32 protein at 37° in the presence of Mg++ . Measurements of infectivity insu - spheroplasts and sedimentation in sucrose demonstrated the formation ofsus + joint molecules from two preparations of sheared λ DNA that carriedsus mutations at opposite ends of the genome. The biological activity of joint molecules made by annealing at 75° was diminished by the addition of the gene-32 protein in the absence of Mg++ , and largely restored by the subsequent addition of Mg++ . The specific infectivity of joint molecules made by gene-32 protein at 37° was similar to that of joint molecules made by annealing at 75°. The experimental system described provides a possible model for simulating early steps in genetic recombination.