SARS Coronavirus Replicative Enzymes: Structures and Mechanisms

The SARS coronavirus (SARS-CoV) replicase gene encodes 16 nonstructural proteins (nsps) with multiple enzymatic activities. Several of these enzymes are common components of replication complexes of other plus-strand RNA viruses, such as picornavirus 3C-like protease, papain-like protease, RNA-dependent RNA polymerase, RNA helicase, and ribose 2′-O-methyltransferase activities, while others such as exoribonuclease, endoribonuclease, and adenosine diphosphate-ribose 1″-phosphatase activities, are rarely or not conserved in viruses outside the order Nidovirales. The latter enzymes are believed to be involved in unique metabolic pathways used by coronaviruses to (1) replicate and transcribe their extremely large RNA genomes, and (2) interfere with cellular functions and antiviral host responses.