The tertiary structure in the 3′-untranslated region (3′-UTR) of Bamboo mosaic virus (BaMV) RNA is known to be involved in minus-strand RNA synthesis. Proteins found in the RNA-dependent RNA polymerase (RdRp) fraction of BaMV-infected leaves interact with the radio labeled 3′-UTR probe in electrophoretic mobility shift assays (EMSA). Results derived from the ultraviolet (UV) cross-linking competition assays suggested that two cellular factors, p43 and p51, interact specifically with the 3′-UTR of BaMV RNA. p43 and p51 associate with the poly(A) tail and the pseudoknot of the BaMV 3′-UTR, respectively. p51-containing extracts specifically down-regulated minus-strand RNA synthesis when added to in vitro RdRp assays. LC/MS/MS sequencing indicates that p43 is a chloroplast phosphoglycerate kinase (PGK). When the chloroplast PKG levels were knocked down in plants, using virus-induced gene silencing system, the accumulation level of BaMV coat protein was also reduced.

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