Zhongguo Xiong
Department of Plant Pathology, University of Arizona
The genome of RCNMV is composed of positive-sense, single-stranded RNA-1 (3.9 kb) and RNA-2 (1.5 kb) . RCNMV genome organization and gene expression strategies have been well characterized by in vitro translation studies , sequencing analysis, and mutagenesis. RCNMV RNA-2 encodes a single p35 movement protein that is required for RCNMV cell-to-cell movement through plasmodesmata. RCNMV RNA-1 contains three open reading frames. They encode, from 5' to 3', p27, p57, and the p37 capsid protein. The first two ORFs (p27 and p57) slightly overlap with each other. A translational ribosomal frameshifting event, similar to that observed in retroviruses, occurs in the overlapping region to generate a p88 fusion protein. This fusion protein consists of the complete p27 as the N-terminal half and p57 as the C-terminal half.
As with other RNA viruses, RCNMV is replicated by an RNA-depedent RNA polymerase (replicase). An active RCNMV replicase has been partially purified. The purified replicase is capable of producing double-stranded RNA products corresponding to RCNMV RNA-1 and RNA-2 in the absence of exogenous templates. The endogenous templates appear tightly bound to the replicase. The double-stranded nature of the replicase products was confirmed by RNase A digestion. The replicase products are double-stranded and are susceptible to RNase A in a low salt solution but are resistant to RNase A in high salt solution. In a denaturing agarose gel, the replicase products behave as full-length genomic RNA and co-migrate with RCNMV RNAs. Northern blot analysis shows that the replicase products are exclusively (+) stranded, suggesting that the replicase-bound template are (-)-strand.
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