Required for aphid transmission and also has proteolytic activity (By similarity). Only cleaves a Gly-Gly dipeptide at its own C-terminus (By similarity). Interacts with virions and aphid stylets (PubMed:9880030). 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 (By similarity). Hydrolyzes a Gly-|-Gly bond at its own C-terminus, commonly in the sequence -Tyr-Xaa-Val-Gly-|-Gly, in the processing of the potyviral polyprotein. The N-terminus is involved in interaction with stylets. The central part is involved in interaction with virions and the C-terminus is involved in cell-to cell movement of the virus. Genome polyprotein of potyviruses undergoes post-translational proteolytic processing by the main proteinase NIa-pro resulting in the production of at least ten individual proteins. The P1 proteinase and the HC-pro cleave only their respective C-termini autocatalytically. 6K1 is essential for proper proteolytic separation of P3 from CI (By similarity). Belongs to the potyviridae genome polyprotein family.