Grapevine fanleaf nepovirus P38 putative movement protein is not transiently expressed and is a stable final maturation product in vivo.

The putative 38 kDa movement protein (P38) gene, located on the RNA2 of grapevine fanleaf nepovirus (GFLV), was cloned in Escherichia coli and expressed as a fusion protein fused to six histidines (6HisP38). This protein was purified and used to produce a specific polyclonal antiserum from which immunoglobulins were isolated by immunoaffinity against the recombinant 6HisP38. Western immunoblot analyses on GFLV RNA2 in vitro maturation products showed that the antibodies were specific for P38 protein. This protein was detected as early as 18 h post-inoculation in GFLV-infected Chenopodium quinoa protoplasts and accumulated to very high levels. Tissue-prints and time course experiments on infected C. quinoa plants confirmed that P38 is present at a high level late in infection and is a final maturation product of the GFLV RNA2 polyprotein in vivo. P94 and P66 intermediates of maturation and polyprotein P2 were also detected in vivo but in very low concentrations. No significant difference was observed in the relative amounts of P66 and P94 detected in vivo, contrary to what occurs in vitro. Subcellular fractionation studies showed that P38, although mainly cytosolic, is also found in association with cell wall and membranes. Thought to be the GFLV movement protein, P38 would thus behave in an 'atypical' manner.