Purity > 85% as determined by SDS-PAGE. MW: 66.6kDa. Partial: 2360-2876aa. N-terminal 10xHis-tagged and C-terminal Myc-tagged. Turnip mosaic virus (strain Japanese) (TuMV). Helper component proteinase: required for aphid transmission and also has proteolytic activity. Only cleaves a Gly-Gly dipeptide at its own C-terminus. Interacts with virions and aphid stylets. Acts as a suppressor of RNA-mediated gene silencing, also known as post-transcriptional gene silencing (PTGS), a mechanism of plant viral defense that limits the accumulation of viral RNAs. May have RNA-binding activity.