Cell-free expression of the coxsackievirus 3C protease using the translational initiation signal of an insect virus RNA and its characterization.

We have expressed the 3C protease of coxsackievirus B3 (CVB3) in a cell-free system. This expression system employs the translational initiation signal of an insect virus RNA, black beetle virus (BBV) RNA 1, to direct CVB3-specific protein synthesis. Using this expression system, we demonstrate that a biologically active 3C protease is synthesized which possesses both cis and trans processing capabilities. This in vitro-synthesized 3C protease is analogous to the native 3C, which was obtained from cytoplasmic extracts of CVB3-infected HeLa cells, in all biological parameters that were evaluated. In addition, antibody prepared against the 3C protease purified from extracts of CVB3-infected HeLa cells cross-reacts with the 3C protease produced in this cell-free system. Using the translational initiation signal from BBV RNA 1, we also have expressed the CVB3 capsid precursor and part of the P2 region in vitro, and have shown that the capsid precursor is cleaved between 1C (VP3) and 1D (VP1) by the proteolytic activity of in vitro-synthesized 3C in trans. Evidence also is presented to implicate the 2A protein of CVB3 as having proteolytic function.