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Fig. 4.
Live-cell and confocal microscopy of the distribution of ECFP-SARS-CoV N protein in cells. Also shown in the confocal image is the expression of DSRedB23.1, a relative fluorescent intensity profile of this cell is also shown. Below are shown live-cell and confocal microscopy of the distribution of ECFP-SARSCoV-NdNES and relative fluorescent intensity are shown. Cells were also co-expressing DsRedB23.1.
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Clearly, SARS-CoV N protein contains amino Platelet Membrane Glycoprotein IIB Peptide (296-306) motifs which would allow its trafficking to the nucleus. Given that this protein is observed in the cytoplasm of infected cells and over-expression studies [21] and [23], the possibility arises that either N protein is inefficiently imported into the nucleus or efficiently exported. The former possibility may occur through structural alteration of the protein exposing the potential NoLS in region II, perhaps through differential phosphorylation or multi-merisation. Deletion and mutagenesis analysis in this and previous studies [20] indicates that the NES motif identified between amino acids 324-EVTPSGTWLT-334 in SARS-CoV N protein is the dominant signal in determining N protein localisation. This motif does not conform to a classical leucine-rich NES and thus represents a novel motif involved in nuclear export.