Model for vaccinia virus DNA replication

Replicating vaccinia DNA molecules synthesized in vivo and in vitro, when examined in the electron microscope, were found to contain dsDNA loops which formed at one end of the molecules. A progressive increase in the size of the loop in individual molecules indicated that chain elongation was occurring. These results suggest that DNA replication was initiated at, and elongation proceeded from, one end of the viral DNA molecules. Based on these observations and previously published biochemical experiments, a model for vaccinia virus DNA replication is proposed.