[Dissolution of polyhedra of the nuclear polyhedrosis virus of the leatherjacket Tipula paludosa MEIG. Ultrastructural study of the virion (author's transl)].

The inclusion bodies of the nuclear polyhedrosis virus of T. paludosa MEIG. were purified by sucrose density gradients, their morphology described using scanning electron microscopy, and the conditions for their solubilization investigated. These inclusions known to be unusually resistant to dissolution, were successfully dissolved in conditions maintaining the integrety of the virus particles by using a 0.125 M sodium thioglycolate + 0.125 M sodium bicarbonate solution, pH 10.5. The virions extracted from the inclusions were purified by sucrose density gradients and their fine structure studied in electron microscopy. In PTA-stained preparations the virion is rod-shaped measuring 230--240 nm in length and 100 to 110 nm in diameter. It consists of an inner nucleocapsid surrounded by a loose envelope. Partially degraded virions reveal small subunits arranged in a regular helix (pitch of approximately 40 A) at the surface fo the capsid. These subunits likely represent the virus capsomers. A flexuous ropelike structure protruding at one end of the capsid is sometimes observed in partially degraded virions stained with uranyl acetate. In thin sections of infected hemocytes, the virions occluded on polyhedra or free in the nucleoplasm exhibit the same morphology although their diameter does not exceed 80--85 nm. The muclear polyhedrosis virus of T. paludosa meets all the criteria for incorporation into the Family Baculoviridae.