In vivo, replication of T7 DNA does not occur after infection of Escherchia coli tsnC mutants (CHAMBERLIN, M. (1974) J. Virol. 14, 509-516). In vitro, extracts of tsnC mutant E. coli infected with T7 hage are incapable of replicating duplex T7 DNA, although extracts of wild type E. coli infected with T7 phage support replication of T7 DNA. In addition, extracts of the infected tsnC mutant are d...