where n N is the stoichiometry of N protein in a single nucleocapsid or virion progeny (Table 2 , [28, 29] ), pol tr and pol lec are the concentrations of the polymerases located on the trailer and complementary leader regions of the genomes and the anti-genomes, respectively, l lec (¼ l l ) is the length of the complementary leader region, and k d,nc is the decay rate constant of nucleocapsid. As progeny virions are assembled, the concentration of each protein is reduced by the amount corresponding to its stoichiometry in a single virion particle.