where p i is the concentration of protein i, k e,rib is the elongation rate of ribosome, l p,i is the length of protein i, and k dp,i is the decay rate constant of protein i. We also accounted for the consumption of free N proteins during the encapsidation of genome-length nascent RNAs and assumed that the degradation of nucleocapsids yielded intact N proteins: dp i dt ¼ k e;rib l p;i rib i À k dp;i p i À n i ðencap Á k e;pol pol tr l tr þ pol lec l lec