MHV virion and MHV genome: (a) electron micrographs of coronavirus particle. (b, c) Schematics of structural protein organization in the MHV virion; MHV virion is somewhat pleomorphic, containing an internal helical RNA genome-nucleocapsid phosphoprotein (N) complex, surrounded by an envelope containing glycoprotein peplomer (S, E, HE, and M) as specified in the text. (d) Organization of the genes in the MHV genome; structural genes are shown in red letters and nonstructural genes in blue letters.