A highly efficient and robust in vitro translation system for expression of picornavirus and hepatitis C virus RNA genomes.

A Krebs-2 cell-free extract that efficiently translates encephalomyocarditis virus (EMCV) RNA and extensively processes the viral polyprotein is also capable of supporting complete infectious EMCV replication. The system displays high RNA synthesis activity and de novo synthesis of virus up to titers of 2 x 10(7) to 6 x 10(7) plaque-forming units (pfu)/ml. The preparation of Krebs-2 cell extract and methods of analysis of EMCV-specific processes in vitro are described. We also demonstrate that the Krebs-2 cell-free system translates the entire open reading frame of the hepatitis C virus (HCV) RNA and properly processes the viral polyprotein when supplemented with canine microsomal membranes. In addition to processing, other posttranslational modifications of HCV proteins take place in vitro, such as the N-terminal glycosylation of the E1 and the E2 precursor (E2-p7) and phosphorylation of NS5A. The HCV RNA-programmed Krebs-2 cell-free extract should prove very useful as a novel screen for drugs that inhibit NS3-mediated processing. The use of this system should help fill the gap in understanding the regulation of synthesis and maturation of HCV proteins. With further optimization of cell-free conditions, the entire reconstitution of infectious HCV synthesis in vitro might become feasible.