N-terminal domains of putative helicases of flavi- and pestiviruses may be serine proteases

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Abstract
Recently we tentatively identified, by sequence comparison. central domains of the NS3 proteins of flaviviruses and the respective portion of the pestivirus polyproteiri as RNA helicaeea (A.E.G. at al., submitted). Alignment of the N-proximal domains of the same proteins revealed conservation of short sequence stretches resembling those around the catalytic Ser, His and Asp residues of chymotrypsin-like proteases. A statistically significant similarity has been detected between the sequences of these domains and those of the C-terminal aerine protease domains of alphavirus capsjd proteins. It is suggested that flavivirus NS3 and the respective peativirus protein contain at least two functional domains, the N-proximal protease and the C-proximal helicase one. The protease domain is probably involved in the processing of viral non-structural proteins.