Specificity and Properties of the Genome-linked Proteins of Nepoviruses

Publisher Website
Google Scholar
Abstract
The infectivity of the RNA of 6 nepoviruses was decreased or abolished by proteinase K treatment, 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, labeled with 125I by the chloramine T method, provided evidence that 3 nepoviruses and Echtes Ackerbohnenmosaik-Virus (EAMV; comovirus group) have genome-linked proteins (VPg). Pronase treatment rendered .apprx. 1/2 (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 RNase P1 yielded a product with an estimated MW of 4000 .+-. 900. Mobilities in polyacrylamide gels of VPg from the RNA of different viruses differed slightly (SLRV > TBRV > TRSV > RRV). TRSV VPg yielded 1 125I-labeled tryptic peptide, the genome-linked proteins of RRV and TBRV both yielded 2 major products, 1 of which was resistant to further digestion and the other was converted, apparently via intermediates, to a 2nd more stable product. No difference was detected between the tryptic peptides obtained from VPg of different strains of RRV or TBRV, or between those obtained from RNA-1, RNA-2 or RNA-3 (satellite RNA) of TBRV. Nepovirus VPg is thus apparently virus-specific. It seems to be coded on RNA-1 and probably has multiple functions.