3C-like protease encoded by Rice tungro spherical virus is autocatalytically processed

The 3C-protease of Rice tungro spherical virus (RTSV) was previously identified as a cis- and trans-acting protease. In vitro translation of the protease resulted in several protein products, demonstrating that the protease is cleaved by itself. The protease was then produced in Escherichia coli as a fusion protein with maltose-binding protein (MBP). Two forms of the protease were purified after MBP affinity chromatography in the column buffer. After analyses of the purified proteins, we speculated that a major internal cleavage site was in the C-terminal half. A point mutation was introduced at a potential major self-cleavage site (C(2763)). The mutation abolished the catalytic activity, suggesting that the mutation site is important for the recognition of the protease.