I. Structural proteins: effects of preparative conditions on the migration of protein in polyacrylamide gels.

Coronavirus A59 possesses four size classes of structural proteins which have apparent molecular weights measured by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of 23,000 (GP23), 50,000 (VP50), 90,000 (GP90), and 180,000 (GP180). VP50 is the only structural protein which is completely unaffected by protease treatment of intact virions. This species is the most highly labeled by polar amino acids such as glutamic acid and arginine and it is probably associated with the viral nucleocapsid. GP90, GP180, and GP23 are membrane-associated proteins. However, after protease treatment of virions, only 20% of the GP23 molecule is digested, whereas all of the GP90 and GP180 are removed. GP90 and GP180 appear to comprise most of the prominent layer of characteristic projections on the external surface of the viral envelope. The major portion of GP23 is presumed to lie within the lipid envelope, protected from protease digestion. GP23 and the protease resistant portion, p18, exhibit anomalous behavior on SDS-PAGE. After heating to 100° in SDS the electrophoretic mobility of these polypeptides is altered and several new forms of lower mobility are produced. β-Mercaptoethanol and dithiothreitol exaggerate the effects of heating.