Development of a nuclear polyhedrosis in cells of Rhynchosciara angelae (Diptera, Sciaridae) and patterns of DNA synthesis in the infected cells

An ultrastructural and autoradiographic study of the infection of cells of Rhynchosciara angelae by a nuclear polyhedrosis virus (RPV) is presented. RPV is a DNA virus and causes a dramatic increase in the volume of the infected cells and in the sizes of chromosomes and their DNA contents. The structure of the nucleoli changes with the infection and the changes are mainly related to an increase of DNA synthesis. The concentration of ribosomes increases in the cytoplasm of the infected cells. Autoradiographic study of the DNA synthesis showed that it varies with the infective process.Four patterns of DNA synthesis, in relation to the host chromosomes and the virus, were disclosed by means of tritiated thymidine incorporation in the infected nuclei. The patterns are: (1) incorporation mainly in the chromosomes, (2) incorporation in the chromosomes and in the nucleoplasm, (3) incorporation only in the nucleoplasm, and (4) incorporation mainly in the chromosomes in dissociation. There is indication of a succession 1→2 and 3→4. The succession of patterns indicates that the virus induces first the increase of synthesis of host cell DNA and RNA. The bulk of the synthesis of viral DNA is evident only after the host cell DNA and RNA machinery is amplified. The aspects of the formation of viral membrane indicate that it is a de novo process in which the membrane material is capable of self-assembly.