Disease relevance of N

• In the murine coronavirus a selective interaction between the viral transmembrane envelope protein M and the viral ribonucleoprotein complex, composed of N protein and viral RNA containing a short cis-acting RNA element, the packaging signal, determines the selective RNA packaging into virus particles [1].
• Further, we found that fusion of domain 3 of the N protein to the carboxy terminus of a heterologous protein caused it to be incorporated into MHV virions [2].
• We have previously shown that SARS-CoV N protein forms a dimer in solution through its C-terminal domain [3].
• Immunoblotting and immunoprecipitation experiments using polyclonal antisera showed that the four major structural proteins of TCV cross-reacted with the four homologous proteins of bovine enteric coronavirus (BCV), the N and M proteins of mouse hepatitis virus serotype 3, and the N protein of IBV [4].
• However, confocal microscopy of N protein localization in Vero cells infected with the severe acute respiratory syndrome coronavirus (SARS-CoV) or transfected with the SARS-CoV N gene failed to show the presence of N in the nucleoplasm or nucleolus [5].

High impact information on N

• Although lacking significant sequence similarity, the dimerization domain of SARS-CoV N protein has a fold similar to that of the nucleocapsid protein of the porcine reproductive and respiratory syndrome virus [3].
• We then examined the -372 to -306 sequence within the 1.3-kb fgl2 promoter region upstream from the transcription start site that was previously identified as necessary for N protein-induced gene transcription [6].
• These data more precisely define the region of the N protein that interacts with the M protein [2].
• The M endodomain interacts with the viral nucleocapsid, which consists of the positive-strand RNA genome helically encapsidated by N protein monomers [2].
• In this report we show that expressed coronavirus envelope protein M specifically interacted with coexpressed noncoronavirus RNA transcripts containing the short viral packaging signal in the absence of coronavirus N protein [1].

Chemical compound and disease context of N

• Here, we characterized temporal changes in N protein-specific and S glycoprotein-specific neutralizing antibody (Nab) responses in infected patients who have either recovered from or succumbed to SARS-CoV infection [7].
• This plasmid containing the N gene was recombined with in a BaculoDirecttrade mark baculovirus DNA designed in order to express N protein in fusion with a C-terminal polyhistidine tag containing V5 epitope [8].

Biological context of N

• In addition, our results suggest that the N protein might function to disrupt cell division [9].
• Coronavirus nucleoproteins (N proteins) localize to the cytoplasm and the nucleolus, a subnuclear structure, in both virus-infected primary cells and in cells transfected with plasmids that express N protein [10].
• The most likely explanation for this is that the N protein induced a cell cycle delay or arrest, most likely in the G(2)/M phase [9].
• The antibody responses to the N protein fragments in mammalian sera revealed that 3 regions of the N protein are strong antigenic domains [11].
• Mutagenesis was used to delineate a novel eight amino acid motif that was necessary and sufficient for nucleolar retention of N protein and colocalize with nucleolin and fibrillarin [12].

Anatomical context of N

• Five independent T-cell clones recognized three separate N-protein domains: 1-133, 134-249, and 250-306 [13].
• Binding of N protein also occurs to membranes in the absence of MHV matrix (M) protein which is known to interact with the N protein [14].
• Binding of N protein to membranes of mouse fibroblast L-2 cells is very specific and occurs under conditions in which no other viral or cellular proteins show detectable binding [14].
• The HE and S glycoproteins were recognized earliest by the bovine immune system while the N protein induced antibody responses during the later stage of initial infection and the early stage of reinfection [15].
• Analysis of synthesized N protein in a nondenaturing gel system showed that it bound in vitro to an endogenous RNA in the reticulocyte lysate but not to its own mRNA [16].

Associations of N with chemical compounds

• The N protein was also shown to bind directly to phospholipid liposomes containing cardiolipin as well as to liposomes containing total lipids extracted from mouse L-2 cells [14].
• Purified N protein was cleaved with formic acid to determine which domain interacts with the leader RNA sequence [17].
• Recovered patients were found to have higher and sustainable levels of both N protein-specific and S glycoprotein-specific Nab responses, suggesting that antibody responses likely play an important role in determining the ultimate disease outcome of SARS-CoV-infected patients [7].
• Recombinant N protein was extracted from infected cells, analysed by SDS-PAGE and Western blot, and purified by Ni(2+) affinity procedure [8].

Physical interactions of N

• Pulse-labeling experiments showed that newly synthesized, unglycosylated M protein interacted with N protein in a pre-Golgi compartment, which is part of the MHV budding site [18].

Other interactions of N

• Analysis of second-site revertants of MDelta2 revealed mutations in the carboxy-terminal region of the N protein that compensated for the defect in the M protein [2].
• By contrast, a VV recombinant encoding a variant non fusogenic S-protein or the N-protein was not capable conferring protection [19].

Analytical, diagnostic and therapeutic context of N

• The N protein of Alb4 was found to be smaller than its wild-type counterpart, and sequence analysis of the Alb4 N gene revealed that it contains an internal deletion of 87 nucleotides, producing an in-frame deletion of 29 amino acids [20].
• Chemical cross-linking and gel-filtration analyses indicated that the residues 283-422 of the SARS-CoV N protein have multimeric ability, although the full-length N protein is prone to exist predominantly as dimers [21].
• All of the Mab recognized both native protein and full-length N protein expressed in this vector by both Western blot and enzyme-linked immunoabsorbent assays (ELISA), indicating that they recognized linear epitopes [22].
• When analysed by ELISA or by immunofluorescence only the antibody response to the N protein was significant; weak responses or no detectable response at all were found for S and M, respectively [23].
• Using previously described BCV primers, the N protein gene of isolate NC99 was amplified by a reverse transcriptase PCR (RT-PCR) procedure [24].

References