A T = 1 capsid formed by protein of brome mosaic virus in the presence of trypsin.

In the presence of trypsin, the coat protein of brome mosaic virus (BMV) has been observed to polymerize in a D2O buffer at pD 7.6 to form a small empty capsid with triangulation number T = 1. Normally, this same protein polymerizes at acidic pH to form empty capsids with T = 3. The trypsin is shown to remove 63 amino acids on the N terminus side leaving a polypeptide chain of Mr 13,500. The kinetics of formation of this small particle have been followed by neutron scattering. Further, the particle has been characterized by various physical methods: analytical centrifugation, quasielastic light scattering, and neutron scattering. It is found to have a radius of about 85-90 A, and a molecular weight of 760,000, in fair agreement with the value expected for a particle made of 60 subunits of 13,500.