- Volume 59, Issue 1, 1982

Transplacental transmission of Japanese encephalitis virus (JEV) has been demonstrated in consecutive pregnancies of mice. Pregnant mice inoculated intraperitoneally with JEV transmit the virus to the foetus. When such female mice were mated again after 6 months, the virus could be isolated from the foetuses of the ensuing pregnancy. The incidence of abortion was increased significantly though the neonatal deaths were considerably less than during the first pregnancy. Intra-uterine infection occurred in spite of the presence of HAI antibodies against JEV in the preconceptional sera of the mice. The findings of the present study indicate the value of such a system for further investigations of the pathogenesis of JEV infection during pregnancy in humans.

The effect of Sindbis virus on cell leakiness, as measured by chromium release, and on the fatty acids in chick embryo fibroblasts and Vero cells was studied. The appearance of the cytopathic effect in both cell types coincided with virus replication, increased cell leakiness and relative increase in saturated eighteen carbon fatty acid (C18:0, stearic acid) compared to the eighteen carbon unsaturated fatty acids (C18UFA). It is postulated that the increase in cell leakiness and the appearance of cytopathic effect could be the result of a physical change in the lipids of the cell membrane brought about by the increase in the saturation of the eighteen carbon fatty acids.

The infectivity of the RNA of six nepoviruses was decreased or abolished by proteinase K treatment, whereas that of the RNA of cowpea mosaic virus (comovirus group) or tomato bushy stunt virus was unaffected. The extent of the decrease in infectivity was characteristic for each nepovirus and was independent of the plant species used as virus source or as assay host. The infectivity of raspberry ringspot virus (RRV) RNA was less affected than that of the other nepoviruses but treatment with Pronase decreased infectivity more than treatment with proteinase K. Proteinase K treatment also abolished the infectivity for tobacco mesophyll protoplasts of RNA of tobacco ringspot virus (TRSV) and tomato black ring virus (TBRV).

Tests on virus RNA, labelled with 125I by the chloramine T method, provided evidence that three nepoviruses and Echtes Ackerbohnenmosaik-Virus (EAMV; comovirus group) have genome-linked proteins (VPg). Pronase treatment rendered about half (RNA of strawberry latent ringspot virus; SLRV), or nearly all (RNA of the other nepoviruses and EAMV), of the 125I soluble in 70% ethanol. Treatment of nepovirus RNA with ribonuclease P1 yielded a product with an estimated mol. wt. of 4000 ± 900. Mobilities in polyacrylamide gels of VPg from the RNA of different viruses differed slightly (SLRV > TBRV > TRSV > RRV). TRSV VPg yielded one 125I-labelled tryptic peptide whereas the genome-linked proteins of RRV and TBRV both yielded two major products, of which one was resistant to further digestion and the other was converted, apparently via intermediates, to a second more stable product. No difference was detected between the tryptic peptides obtained from VPg of different strains of RRV, or of TBRV, or between those obtained from RNA-1, RNA-2 or RNA-3 (satellite RNA) of TBRV. Nepovirus VPg is therefore virus-specific. It seems to be coded on RNA-1 and probably has multiple functions.

RNA extracted from particles of potato leafroll virus (PLRV) infected tobacco mesophyll protoplasts. Treating the RNA with proteinase K did not abolish its infectivity. In messenger-dependent rabbit reticulocyte lysate, PLRV RNA induced the synthesis of specific polypeptides: a major product of mol. wt. 71000 but no product the size of coat protein. PLRV RNA is therefore positive-stranded. A genome-linked protein (apparent mol. wt. 7000) was detected in preparations of PLRV RNA but no polyadenylate sequence was found. These features may prove to be characteristic of luteoviruses.

A hitherto uncharacterized nucleoprotein sedimenting at 95S to 99S has been observed in preparations of six different isolates of strawberry latent ringspot virus when centrifuged in sucrose-density gradients. This component had the same coat protein composition, serological properties, size and outward aspect of particles as the rest of the virus and encapsidated a molecule of RNA-2, thus exhibiting all major characteristics of the middle (M) component of nepoviruses. One of the virus isolates under study, as well as two functional RNA species, appeared to possess a third satellite-like RNA with mol. wt. 0.45 × 106.