STRUCTURES DERIVED FROM COWPEA CHLOROTIC MOTTLE AND BROME MOSAIC VIRUS PROTEIN

The behavior at different salt and acidic pH levels of protein isolated from three spherical plant viruses was investigated. Broad bean mottle virus protein did not aggregate into recognizable organized structures. Protein from brome mosaic virus formed capsids similar to those of the virus at a pH and salt-dependent efficiency with best yields at pH 5.0 in 0.2 M NaCl. Best yields for cowpea chlorotic mottle virus protein capsids occurred at pH 5.0 in 0.1 M NaCl or from pH 3.5 to 5.0 in 0.2 M NaCl. Protein from the latter virus also formed double-shelled and rosettelike particles in 0.2 M NaCl from pH 5.3 to 5.7. Narrow tubes were made at pH levels of 6.0 and higher, and the tubes were accompanied by T = 1 and T = 3 particles if ribonu-clease-digested RNA was present. In the absence of NaCl in 0.01 M acetate buffer at pH 4.0 and 4.5, laminar and platelike aggregates were found with CCMV protein. The production and some of the properties of the various forms are described. © 1969.