Figure 1. An introduction to CPMV.

(a) Schematic of the Cowpea mosaic virus (CPMV) bipartite, positive-sense single-stranded RNA genome. RNA-1 is 6 kb in length and contains the non-structural genes, while RNA-2 is 3.5 kb in length and contains the sequence encoding the large coat protein (L subunit) and small coat protein (S subunit). Hypertranslatable constructs (HT) separately expressing the viral proteinase and the precursor of the L and S subunits are used for production of eVLPs using the pEAQ vector system. (b) The sequence of S subunit amino acids 180–213. The C-terminal 24 amino acid segment of S subunit is cleaved following assembly, and is coloured magenta. The cleavage site between Leu189 and Leu190 is shown. This region of the polypeptide is highly positively charged and the positive amino acids are indicated. (c) Schematic of CPMV density purification. RNA-1 containing CPMV sediments at the bottom of a Nycodenz gradient (CPMV-B), RNA-2-containing CPMV (CPMV-M) sediment in the middle and empty CPMV particles sediment at the top of the gradient (CPMV-T). CPMV-T particles are the natural equivalent to empty virus-like particles (eVLPs). (d) X-ray crystal structure of the asymmetric unit of CPMV (PDB 1NY7⁴), coloured as above. The C-terminal amino acid of the S subunit (leucine 189) is indicated. (e) Icosahedral organization of CPMV (using PDB 1NY7⁴). Each icosahedral particle is comprised of 60 copies of both the L subunit and the S subunit. A view down the twofold axis is shown.