where pol r,n,N,1 is the concentration of the replicating polymerases on the first segment of the N gene section in the negative-sense genomic nucleocapsid. dpol r;n;i;1 dt ¼ k e;pol ðencap n sec;iÀ1 l mRNA;iÀ1 pol r;n;iÀ1;nsec;iÀ1 À n sec;i l mRNA;i pol r;n;i;1 Þ i ¼ P; M; G; L ð16Þ