Minor base sequence differences between the genomes of two strains of murine cytomegalovirus differing in virulence.

Two strains of murine cytomegalovirus (MCMV), differing in virulence towards mice, were compared for possible genetic differences. The two strains behaved identically in cell cultures, although the virulent strain gave higher yields of infectious virus in salivary glands. The viral DNAs displayed identical reassociation kinetics, but minor differences in their base sequences were revealed by restriction endonuclease profiles. The endonuclease profile of the "virulent" strain was conserved during serial high multiplicity infection in vitro.