Abstract
1 Institute of Molecular Biology,
2 Institute of Microbiology, Russian Academy of Sciences, Moscow, Russia
3 National Center for Biotechnology Information, National Library of Medicine, Building 38A, National Institutes of Health, 8600 Rockville Pike, Bethesda, Maryland 20894, U.S.A.
and4 Institute of Poliomyelitis and Viral Encephalitides, Russian Academy of Medical Sciences, Moscow Region, Russia.
Computer-assisted comparisons of the large proteins involved in the replication of viral RNA have revealed a novel domain located near the N termini of these proteins and conserved throughout the so-called Sindbis-like supergroup of positive-strand RNA viruses. This domain encompasses four distinct conserved motifs, with motifs I, II and IV containing an invariant His residue, the AspXXArg signature and an invariant Tyr residue, respectively. Each of the two large groups of viruses within this supergroup, the altovirus group (alphaviruses, tobamoviruses, tobraviruses, hordeiviruses, tricornaviruses, furoviruses, hepatitis E virus and probably rubiviruses), and the typovirus group (tymoviruses, potexviruses, carlaviruses and apple chlorotic leaf spot virus), can be characterized by additional conserved sequence motifs. Based on the available results of biochemical studies and site-directed mutagenesis of the alphavirus proteins, it is hypothesized that this domain may be involved in methylation of the cap during viral RNA maturation. Unlike the other conserved domains, the RNA-dependent RNA polymerase and the RNA helicase, the motifs typical of the putative methyltransferase domain are universal within the Sindbis-like supergroup but are not found in the proteins of any other viruses, constituting a distinctive hallmark of this supergroup.
† Present address: Institut Jacques Monod, 2 Place Jussieu, 75251, Paris cedex 05, France.