Circular replicating baculovirus genome

: Free Malacosoma neustria nuclear polyhedrosis virus preparations contain nucleocapsids typical of Baculoviruses' morphology and size as well as long virus-like particles. Viral DNA is circular and covalently closed. Its preparations contain rings with single-stranded breaks, catenanes and circular dimers as well. Replicating pulse-labelled DNA preparations have been obtained from cells with the highest virus DNA synthesis. Theta-forms of replicating DNA are found in heavy fractions of sucrose gradients. Theta-forms, catenanes and circular dimers are discussed as intermediate molecules. Catenanes or (sometimes) circular dimers appear to form protein-containing complexes and long virus-like particles if the monomerization process is inhibited.