Disease relevance of nsP1

• Reaction in alphavirus mRNA capping: formation of a covalent complex of nonstructural protein nsP1 with 7-methyl-GMP [1].
• Further evidence for the contribution of nsP1 Thr 538 to S.A.AR86 neurovirulence was provided by experiments in which a threonine residue was introduced at nsP1 position 538 of Sindbis virus strain TR339, which is nonneurovirulent in weanling mice [2].
• This finding agrees with data obtained with Ross River virus and contrasts with the well-studied Sindbis alphavirus major packaging signal that is located within the nsP1 gene [3].
• The nonstructural (ns) proteins nsP1 to -4, the components of Semliki Forest virus (SFV) RNA polymerase, were localized in infected cells by confocal microscopy using double labeling with specific antisera against the individual ns proteins [4].
• Recombinant nsP1 was expressed in Escherichia coli and partially purified by flotation in a discontinuous sucrose gradient [5].

High impact information on nsP1

• The reaction was specific for guanylate nucleotides (GTP, dGTP) and was inhibited by pyrophosphate. nsP1 could be labeled with S-adenosyl[methyl-3H]methionine but only under conditions in which the nsP1-guanylate complex was formed [1].
• Site 2/3 was cleaved rapidly in trans but only after release of nsP1 from the polyprotein exposing an "activator" sequence present in the amino terminus of nsP2 [6].
• The Sindbis-group alphavirus S.A.AR86 encodes a threonine at nonstructural protein 1 (nsP1) 538 that is associated with neurovirulence in adult mice [7].
• We suggest that the spherules arise by primary assembly of the RNA replication complexes at the plasma membrane, guided there by nsP1, which has affinity to lipids specific for the cytoplasmic leaflet of the plasma membrane [4].
• The membrane-associated alphavirus RNA replication complex contains four virus-encoded subunits, the nonstructural proteins nsP1 to nsP4 [8].

Chemical compound and disease context of nsP1

• S.A.AR86, a member of the Sindbis group of alphaviruses, is neurovirulent in adult mice and has a unique threonine at position 538 of nsP1; nonneurovirulent members of this group of alphaviruses encode isoleucine [2].

Biological context of nsP1

• When mutations preventing nsP1 palmitoylation were introduced into the genomes of these two alphaviruses, the mutant viruses remained viable and replicated to high titers, although their growth was slightly delayed [8].
• The nsP1 palmitoylation-defective alphaviruses produced normal plaques in several cell types, but failed to give rise to plaques in HeLa cells, although they induced normal apoptosis of these cells [8].
• Between the complete nucleotide sequences of the full-length cDNA clone, pSAG2, and the consensus sequence from the original stock virus, there were nine amino acid differences; two each in nsP1, nsP2 and E1, and three in E2, some of which may be responsible for plaque phenotypic variants in the original virus stock [9].
• The membrane association may be due to acylation, since nsP1 could be labeled with [3H]palmitic acid in both Semliki Forest virus-infected and nsP1-transfected HeLa cells [10].
• Membrane association of nsP1, and its affinity to endosomes and lysosomes, suggest a role of this protein in the biogenesis of the alphavirus-specific RNA replication complex [10].

Anatomical context of nsP1

• Later, nsP1 appeared on large vacuoles, which contained the lysosome specific h-lamp-1 protein [10].
• The alphavirus replicase protein nsP1 is membrane-associated and has affinity to endocytic organelles [10].

Associations of nsP1 with chemical compounds

• A replicase containing nsP1, P23, and nsP4 can make both plus and minus strands, but prefers the promoter for genomic plus sense RNA to that for subgenomic mRNA [11].
• Release of the 3H-label by alkaline methanolysis suggests that the palmitate was associated with nsP1 via an ester bond [10].

Physical interactions of nsP1

• The results from this study and from a previous report on the shutoff of minus-strand RNA synthesis at 40 degrees C with the nsP1-A348T mutation in ts11 suggests that the N-terminus nsP4 interacts with nsP1 during initiation of minus-strand RNA synthesis [12].

Other interactions of nsP1

• Antibodies specific for nsP3, and to a lesser extent antibodies to nsP1, precipitated native replication complexes that retained prelabeled RIs and were active in vitro in viral RNA synthesis [13].

Analytical, diagnostic and therapeutic context of nsP1

• Using the reverse transcription-polymerase chain reaction (RT-PCR) and direct sequencing, capsid protein and non-structural protein 1 (nsP1) regions of Sagiyama virus and eight Getah virus strains were analysed [14].

References