THE N-TERMINAL PROTEIN OF THE POLYPROTEIN ENCODED BY THE POTYVIRUS TOBACCO VEIN MOTTLING VIRUS IS AN RNA-BINDING PROTEIN

The first predicted polypeptide encoded by the potyvirus tobacco vein mottling virus (TVMV) is a highly positively charged protein of predic ted M(r) 29K that functions as a protease to perform the first predict ed cleavage in the potyvirus polyprotein. We expressed this protein (P 1pro) fused with glutathione S-transferase (GST) and purified the fusi on protein from engineered Escherichia coli. We found that the intact fusion protein, as well as samples in which the P1pro portion was libe rated from GST by pretreatment with thrombin, was able to bind RNA. Bi nding activity was optimal at relatively high KCl concentrations, sugg esting an interaction dependent on a specific protein structure and no t just on the binding of the negatively charged phosphate backbone by the positively charged P1pro polypeptide. The TVMV P1pro preferred ssR NA over DNA or dsRNA, and showed a possible preference for sequences c ontaining oligo(G) tracts. Like other potyvirus-encoded proteins, the TVMV P1pro therefore possesses more than one demonstrable biochemical activity and probably plays multiple roles in the TVMV life cycle.