Characterization of chimeric turnip yellow mosaic virus genomes that are infectious in the absence of aminoacylation.

摘要

Turnip yellow mosaic tymovirus (TYMV) sequences were introduced into the anticodon loop and amino acid acceptor arm of the chimeric genome TYMC-TMVPSK, in which the 3'-tRNA-like structure of TYMV was replaced by 3' sequences from tobacco mosaic tobamovirus. This led to 3- and 4-fold increases in viral accumulation. Two such modified chimeric genomes gave rise to stable infections in plants. After further passaging in plants and the accumulation of minor sequence changes in the 3' terminal region, the resultant viruses, TYMC-XX and TYMC-YY, were highly infectious. Viral accumulations in protoplasts were c. 40% of wild type on the basis of coat protein levels and virion yields in plants were c. 0.1 mg/g leaf. Extensive assays failed to detect aminoacylation of these genomic RNAs in vitro, but they were active substrates for wheat germ CCA nucleotidyltransferase. In separate experiments, the 3'-tRNA-like structure of TYMV RNA was replaced by the 3' terminal 96 nucleotides from erysimum latent tymovirus RNA, resulting in a genome that was infectious to plants (isolate TYMC-H). This chimeric virus produced similar symptoms and virion yield in plants as TYMC-XX and -YY, although accumulations of coat protein in protoplasts were 13% of wild type. The viral RNA was a poor substrate for CCA nucleotidyltransferase and could not be aminoacylated. TYMC-XX, -YY and -H were the first TYMV replicons known to amplify efficiently and infect plants in the absence of aminoacylation.