DNA polymerase alpha-primase complexes in extracts of MVM-infected murine cells were dissociated in the presence of 0.3M KCl to generate a 12S DNA primase and a 10S DNA polymerase alpha that were readily separated by sedimentation in glycerol gradients. A 12S DNA polymerase alpha-primase complex refractory to dissociation in 0.3M KCl was identified in extracts of MVM-infected HeLa cells. In extracts of mock-infected murine and HeLa cells DNA primase and DNA polymerase alpha were not dissociated from each other in 0.3M KCl but remained in a stable complex that sedimented at 10S. We propose that a novel 12S DNA polymerase alpha-primase complex prone to disruption by salt is induced by MVM infection and that the DNA primase component of the complex is modified.