Molecular Recombination in T4 Bacteriophage Deoxyribonucleic Acid: III. Formation of Long Single Strands During Recombination.

Evidence was presented to support the hypothesis that long single strands appearing at late times (15 min after infection) are produced as a result of recombination and not as a continuous elongation during the replication process. The production of long strands does not depend on the multiplicity of infection, and the first long strands appear at the time when 20 to 50 phage equivalent units of deoxyribonucleic (DNA) are synthesized, and not earlier. The addition of chloramphenicol at 5 min, which prevents molecular recombination but allows replication of DNA, prevents the formation of long, single strands. Chloramphenicol added between 8 and 10 min after infection, a time at which molecular recombination is fully expressed and covalent repair of recombinant molecules is allowed, does not prevent formation of long single strands. Cutting of single-strand DNA with a limited amount of endonuclease I allows confirmation that the fast-sedimenting characteristic of intracellular denatured DNA is caused primarily by the length of the strands, and not by the formation of aggregates. The computer simulation of two recombination models indicates the feasibility of random breakage and rejoining of molecules in generating long concatenates.