Hepatitis C VirusNS3Protein Polynucleotide-Stimulated Nucleoside Triphosphatase andComparison withtheRelated Pestivirus andFlavivirus Enzymes

NTPaseactivity. Characterization ofthepurified HCV NTPaseactivity showed that itexhibited reaction condition optimawithrespect topH,MgCl2,andsaltidentical tothoseofthe representative pestivirus andflavivirus enzymes.However, eachNTPasealsopossessed several unique properties whencompared with oneanother. Notably, theprofile ofpolynucleotide stimulation oftheNTPase activity was distinct forthethree enzymes.TheHCV NTPase was theonlyonewhoseactivity was significantly enhanced bya deoxyribopolynucleotide. Additional distinguishing features among thethree enzymesrelating tothekinetic properties oftheir NTPaseactivities are discussed. Thesestudies provide a foundation for investigation oftheputative RNA helicase activity ofthese proteins andforfurther study oftherole oftheNS3 proteins ofmembersoftheFlaviviridae inthereplication cycle ofthese viruses.