Endodeoxyribonuclease I, which is expressed in the late stage, is necessary for T3 genetic recombination and the breakdown of host DNA. In the early stage of infection, T3 DNA replicates as a linear monomer. In the late stage, the T3 DNA replicates via linear concatemers several genomes in length. The gene 3 product has also been implicated in the maturation of these concatemers. Endonucleolytic cleavage to 5'-phosphooligonucleotide end-products.