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Protein Domain : RNA-directed RNA polymerase, rhabdovirus

Primary Identifier  IPR017234 Type  Family
Short Name  RNA-dir_pol_rhabdovirus
description  RNA-directed RNA polymerase (RdRp) () is an essential protein encoded in the genomes of all RNA containing viruses with no DNA stage [, ]. It catalyses synthesis of the RNA strand complementary to a given RNA template, but the precise molecular mechanism remains unclear.The postulated RNA replication process is a two-step mechanism. First, the initiation step of RNA synthesis begins at or near the 3' end of the RNA template by means of a primer-independent (de novo) mechanism. The de novo initiation consists in the addition of a nucleotide tri-phosphate (NTP) to the 3'-OH of the first initiating NTP. During the following so-called elongation phase, this nucleotidyl transfer reaction is repeated with subsequent NTPs to generate the complementary RNA product []. All the RNA-directed RNA polymerases, and many DNA-directed polymerases, employ a fold whose organisation has been likened to the shape of a right hand with three subdomains termed fingers, palm and thumb []. Only the catalytic palm subdomain, composed of a four-stranded antiparallel β-sheet with two α-helices, is well conserved among all of these enzymes. In RdRp, the palm subdomain comprises three well conserved motifs (A, B and C). Motif A (D-x(4,5)-D) and motif C (GDD) are spatially juxtaposed; the Asp residues of these motifs are implied in the binding of Mg2+ and/or Mn2+. The Asn residue of motif B is involved in selection of ribonucleoside triphosphates over dNTPs and thus determines whether RNA is synthesised rather than DNA [].The domain organisation []and the 3D structure of the catalytic centre of a wide range of RdPp's, even those with a low overall sequence homology, are conserved. The catalytic centre is formed by several motifs containing a number of conserved amino acid residues.There are 4 superfamilies of viruses that cover all RNA containing viruses with no DNA stage:Viruses containing positive-strand RNA or double-strand RNA, except retroviruses and Birnaviridae: viral RNA-directed RNA polymerases including all positive-strand RNA viruses with no DNA stage, double-strand RNA viruses, and the Cystoviridae, Reoviridae, Hypoviridae, Partitiviridae, Totiviridae families.Mononegavirales (negative-strand RNA viruses with non-segmented genomes).Negative-strand RNA viruses with segmented genomes, i.e. Orthomyxoviruses (including influenza A, B, and C viruses, Thogotoviruses, and the infectious salmon anemia virus), Arenaviruses, Bunyaviruses, Hantaviruses, Nairoviruses, Phleboviruses, Tenuiviruses and Tospoviruses.Birnaviridae family of dsRNA viruses.The RNA-directed RNA polymerases in the first of the above superfamilies can be divided into the following three subgroups:All positive-strand RNA eukaryotic viruses with no DNA stage.All RNA-containing bacteriophages -there are two families of RNA-containing bacteriophages: Leviviridae (positive ssRNA phages) and Cystoviridae (dsRNA phages).Reoviridae family of dsRNA viruses.This entry represents RNA-directed RNA polymerase (also known as the large structural protein) from various Rhabdoviruses, such as Vesicular stomatitis Indiana virus []. The large structural protein (or L protein) carries four enzymatic activities: RNA-directed RNA polymerase (), mRNA (guanine-N(7)-)-methyltransferase (), mRNA guanylyltransferase (), and poly(A) synthetase. The viral mRNA guanylyl transferase displays a different biochemical reaction than the cellular enzyme. The template is composed of the viral RNA tightly encapsidated by the nucleoprotein (N). The protein can function either as transcriptase or as replicase. The transcriptase synthesises subsequently five subgenomic RNAs, assuring their capping and polyadenylation by a stuttering mechanism. The replicase mode is dependent on intracellular N protein concentration. In this mode, the polymerase replicates the whole viral genome without recognizing the transcriptional signals.

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