A human coronavirus, strain OC 43, was propagated in suckling mouse brain and purified 5000-fold with, a 90% yield. Purity of the virus was confirmed by electrophoretic, ultracentrifugal, and electron microscopic procedures. Immunodiffusion and immunoelectrophoresis tests revealed one precipitin line with normal mouse brain, three with purified virus, and four with crude virus when tested against anti-pure virus or anti-crude virus animal serums. The association of a host cell antigen with the virion was confirmed by standard HI and CF tests. Polyacrylamide gel electrophoresis of solubilized purified virus revealed a minimum of six polypeptides with apparent molecular weights of 191,000 (No. 1), 104,000 (No. 2), 60,000 (No. 3), 47,000 (No. 4), 30,000 (No. 5), and 15,000 daltons (No. 6). A seventh band was occasionally found in the 165,000-dalton region of the gels. Four polypeptides contained carbohydrate and one contained lipid. Polypeptide No. 5 comprised 26% of the total viral protein and glycopolypeptide No. 3 comprised 23%. Three other components accounted for most of the remaining protein: polypeptide No. 4 (16%), glycopolypeptide No. 6 (14%), and glycolipopolypeptide No. 1 (13%). Glycopolypeptide No. 2 was 8% of the total protein. Bromelin digestion of the viral projections (spikes) removed glycopolypeptides No. 2 and No. 6. Association of the remaining polypeptides with structural components of the virion is only tentatively postulated. The buoyant density in potassium tartrate of the bromelin-treated virus was 1.15 g/cm3 and of the intact OC 43 virion was 1.18 g/cm3. By analytical ultracentrifugation the corrected sedimentation coefficient (s 0 20w) of the OC 43 virion was determined to be 390 ± 16 S, and the apparent molecular weight (MW a ) was calculated to be 112 ± 5 × 106 daltons.
