Assembly of a spherical plant virus

Abstract

The conditions previously reported as necessary for the reassembly of spherical viruses were distinctly unphysiological and such reassembly cannot be related directly to the in vivo reaction. Mild conditions for the in vitro reassembly of cowpea chlorotic mottle virus (CCMV) from its isolated components were now described and the reassembled virus characterized. This reassembly involved the co-aggregation of the RNA and protein around neutrality and at ionic strengh 0.2, giving yields of 70% encapsidation at pH 6.0. The reaction was independent of temperature over the range 5-25.degree. C and did not require the presence of Mg2+ ions. The reassembled virus shows a stability similar to that of native CCMV, with the same change in sedimentation coefficient around pH 6.5. The molecular mass and buoyant density in CsCl are also the same as those of native CCMV, while EM reveals a surface morphology on the reassembled particles like that on native CCMV. Analysis of the number-average, mass-average and Z-average molecular masses of the purified protein at pH 6.0 and 7.5 suggests that the active unit for reassembly is a dimer of the protein subunit.