Biochemical Studies of Virus Reproduction

Direct chemical evidence has shown that the infecting bacterial virus particle is extensively broken down during the reproductive process (1,2). This finding supports the interpretation of various studies of bacteriophage reproduction by geneticists, who have postulated that the virus is broken down to smaller units shortly after infection (3-6). The disruption of the virus particle upon infection of the host cell has also been suggested for the vaccinia, influenza, and psittacosis systems, because in all these cases it is not possible to recover more than a small fraction of the active virus from the infected cell in the initial stages of infection (7-9). Probably the observed breakdown of the bacteriophage particle is only an example of a general phenomenon involved in the reproduction of most viruses. In an earlier investigation (1) Putnam and Kozloff infected Escher&%&z coli cells with P32-labeled bacteriophage T& and measured the distribution of the isotope in the final lysate. Most of the isotope was found in nonviral soluble fractions, but about one-third of the isotope was found in the viral progeny. More recently Lesley, French, Graham, and van Rooyen (2) have found that P32-labeled T2r+ bacteriophage is broken down following the infection of the host cell, and t,hey have carried on kinetic studies of the process. Experiments have now been performed with N15-labeled bacteriophage Tsr+ and with phage doubly labeled with N15 and P32. It has been found that the protein portion of the virus, as well as the nucleic acid portion, is broken down during the reproductive process. However, a small fraction of the parent virus nucleic acid and protein N is contributed to the progeny. Experiments bearing on the mechanism of the contribution of the parent virus material to the progeny are presented in another paper (10).