Purification of measles virus and characterization of subviral components

Purified measles virus was obtained from [35S]methionine-labeled cells infected at 33 degrees C and maintained in the absence of fetal calf serum. The pellet that was produced by a single high-speed ultracentrifuge spin of culture medium contained virus of purity sufficient for structural analysis. Purified virions contain seven polypeptides with estimated molecular weights of: L, 200,000; G, 80,000; P2, 70,000; NP, 60,000; A, 43,000; F1, 41,000; and M, 37,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Treatment of virions with 0.25% trypsin resulted in a less dense particle which lacked polypeptides G and F1. Solubilization of the viral membrane with the detergent Triton X-100 in low-salt buffer resulted in the loss of the G polypeptide, whereas in the presence of 1 M KCl, Triton X-100 also removed most of the M polypeptide. The nucleocapsids (p = 1.3) obtained from virions treated with Triton X-100 and 1 M KCl contained the L, P2, NP, and M polypeptides. Nucleocapsids isolated from the cytoplasm of infected cells were predominantly composed of the NP polypeptide with smaller amounts of either polypeptide P2 or novel polypeptides, related to NP, with estimated molecular weights of 56,000 to 58,000 and 45,000 to 46,000. A significant amount of polypeptide L was always found in association with nucleocapsids isolated either from virions or from the cytoplasm of infected cells. A membrane component containing the viral membrane polypeptides G, F1, and M was also isolated from infected cells. The data presented here thus suggest that L is an integral part of the nucleocapsid complex. In addition, 37,000-molecular-weight polypeptide (M) appears to have the function described for the matrix proteins of other paramyxoviruses.