Low-multiplicity infection of Moloney murine leukemia virus in mouse cells: effect on number of viral DNA copies and virus production in producer cells.

Mouse cells infected with Moloney murine leukemia virus (M-MuLV) were prepared by two methods, and the number of M-MuLV-specific DNA copies in the infected cells was measured. The number of M-MuLV-specific DNA copies detected varied from one to eight per infected cell in different cell lines. Cells in which multiple rounds of viral infection occurred during establishment had on the average more viral DNA copies than cells in which infection at low multiplicity was performed, followed by cloning of the cells. However, even in cells derived by the low multiplicity of infection method, most cell lines carried more than one copy of M-MuLV-specific DNA. Virus production per cell was also measured, and no strict correlation was observed between the number of M-MuLV DNA copies present and the amount of virus produced.