Envelope and nucleoid ultrastructure of Molluscum contagiosum virus.

The ultrastructure of the mature and immature poxvirus Molluscum contagiosum has been examined by electron microscopy. With freeze-fracturing one fracture plane was observed in the viral envelope. During the conversion of immature into mature virus, particles inside the envelope become partly rearranged into parallel bands. Depressions in freeze-fractured cores of mature particles suggest the presence of water-rich regions. The organization of the nucleoid was investigated by thin sections analyzed in a tilting rotating specimen stage. The nucleoid consists of fibers with a diameter of approximately 10 nm which are probably connected to each other, thus forming one long fiber. In thin sections four profiles of the nucleoid were observed which were transformed into one another by tilting. Serial sections together with tilting revealed a twist of about 180 degrees between the fibers of the two lobules of the nucleoid. A model for the conformation of the nucleoid in the mature brickstone particles is presented.