PROCESSING AND EVOLUTION OF THE N-TERMINAL REGION OF THE ARTERIVIRUS REPLICASE ORF1A PROTEIN - IDENTIFICATION OF 2 PAPAINLIKE CYSTEINE PROTEASES

Two adjacent papainlike cysteine protease (PCP) domains, PCP alpha and PCP beta, were identified in the N-terminal region of the open readin g frame la replicase proteins of the arteriviruses porcine reproductiv e and respiratory syndrome virus and Lactate dehydrogenase-elevating v irus. The replicase of the related virus equine arteritis virus contai ns only one active PCP in the corresponding region. Sequence compariso n revealed that the equine arteritis virus PCP alpha counterpart proba bly was inactivated by loss of its catalytic Cys residue. For both por cine reproductive and respiratory syndrome virus and lactate dehydroge nese-elevating virus, the generation of two processing products, nsp1 alpha and nsp1 beta, was demonstrated by in vitro translation. Site-di rected mutagenesis and sequence comparison were used to identify the p utative active-site residues of the PCP alpha and PCP beta protease do mains and to show that they mediate the nsp1 alpha/1 beta and nsp1 bet a/2 cleavages, respectively.