Disease relevance of NIb

• Uridylylation of the potyvirus VPg by viral replicase NIb correlates with the nucleotide binding capacity of VPg [1].
• The foreign sequences are cloned between the NIb replicase and capsid protein (CP) cistrons [2].
• In a previous study, we showed that transgenic Nicotiana benthamiana NIbV3 plants, transformed with a mutated NIb coding sequence from Plum pox virus (PPV), showed a delayed, very specific, resistance phenotype, which was induced by the initial infection [3].
• The potato A potyvirus (PVA)-encoded proteins P1, HC-Pro, P3, CI, VPg, NIaPro, NIb and coat protein (CP) were expressed as 6 x His-tagged recombinant proteins in Escherichia coli and purified to homogeneity [4].
• The sequence is consistent with the NIb and coat protein regions of a member of the Potyviridae family of viruses [5].

High impact information on NIb

• A genetic complementation system was developed in which tobacco etch virus (TEV) polymerase (NIb)-expressing transgenic plants or protoplasts were inoculated with NIb-defective TEV mutants [6].
• The nucleotidylation activity of NIb is more efficient in the presence of Mn(2+) than Mg(2+) and does not require an RNA template [1].
• These results support the hypothesis that interaction between NIa and NIb is important during TEV genome replication [7].
• Self-interactions manifested by VPg and HCPro and an interaction between NIb and NIaPro were observed in ClYVV [8].
• The results of this study indicate that NIaPro catalyses proteolytic cleavages preferentially in cis, and that the 6K1/CI and NIb/CP sites can also be processed in trans [9].

Chemical compound and disease context of NIb

• Glutamate at the -1 position has also been observed at the CI/NIa-VPg junction of pea seed borne mosaic virus and turnip mosaic virus and at the NIb/CP junction of papaya ringspot virus polyproteins [10].

Biological context of NIb

• Analysis of the amino acid sequences of OMV and other potyvirus proteins showed similarities of 66% to 77% for CP, 72% to 73% for NIb and 63% to 71% for NIa proteins [11].
• PSbMV-NY varied between experiments in its ability to induce resistance, suggesting that the sequence identity in the NIb gene is borderline for the specificity required for triggering gene silencing [12].
• Insertions of Pro-Pro dipeptides, which were predicted to induce protein folding aberrations, at three out of four positions in NIb reduced translocation [13].
• To understand the possible relationship between NIb nuclear localization and its function, we have studied translocation of NIb using gene fusion and plant transformation techniques [13].
• Likewise, the region of the NIb gene sequenced shows 99% and 97% sequence identity in the deduced amino acid and the nucleotide sequences, respectively [14].

Anatomical context of NIb

• Mutational analyses were carried out to investigate whether the nuclear inclusion protein a (NIa) C-terminal amino acids of turnip mosaic potyvirus play any roles in the cis-cleavage between NIa and NIb [15].
• However, their ability to react against NIb was greatly altered. scFv2A fragments were transiently expressed in the cytosol of Nicotiana benthamiana and although they accumulated to low levels, inhibition-ELISA results indicated that they retained antigen-binding activity [16].
• Furthermore, amorphous cytoplasmic inclusions induced by papaya ringspot virus contained the expected HC-Pro but additionally NIa, NIb and CI [17].

Associations of NIb with chemical compounds

• Mutation of a highly conserved glutamic acid residue in the putative pRb-binding motif of the NIb had no detectable phenotypic effect on replication of Potato virus A (PVA) [18].
• Only two of these differences are likely to be functionally important (His rather than Gln at position1217 in the VPg cistron; His rather than Asp at position 1776 in the NIb cistron) [19].

Other interactions of NIb

• TEV NIs are known to contain a bifunctional genome-linked protein-viral proteinase (NIa-VPg) and RNA-dependent RNA polymerase (NIb) [20].
• In the YTHS, P1 interacted only with CI and P3 with NIb [21].
• To identify further these potyviruses, sequences located between the 3' end of the NIb gene and the 5' end of the CP gene were chosen to design a series of species-specific probes [22].
• Beet mosaic virus-induced nuclear inclusions ('satellite bodies') contained in their electron-dense matrix NIa, NIb, Hc-Pro and CI and in their lacunae CP in bundles of virion-like filaments [17].

Analytical, diagnostic and therapeutic context of NIb

• To investigate the significance of this interaction, a Saccharomyces cerevisiae two-hybrid assay was used to isolate conditional NIa mutant proteins with temperature-sensitive (ts) defects in interacting with NIb [7].
• This fusion protein was able to recognise viral NIb in both Western and tissue-print ELISA blots [16].
• The 3' end of the viral genome encompassing the 3' non-coding region, the coat protein gene, and part of the NIb gene was amplified from infected leaf material by IC/PCR using degenerate and specific primers [23].
• A reverse transcription polymerase chain reaction (RT-PCR) protocol was developed using two 20-mer primers located in nuclear inclusion genes NIa and NIb of potato virus Y (PVY) [24].
• Sequence analysis was used to design a pair of degenerate oligonucleotide primers that amplified a 1.6-2.1 kbp fragment from the 3' end of the genome (virion protein gene and part of the NIb gene) of 17 species of the Potyviridae ('potyvirids'); 11 potyviruses, 2 bymoviruses, 2 macluraviruses, an ipomovirus and a rymovirus [25].

References