where rib i is the concentration of the ribosomes assigned to mRNA i. The synthesis rate of each viral protein depends on the elongation rate of the ribosome, linear density of ribosomes on its corresponding mRNA, and its first-order decay rate: dp i dt ¼ k e;rib l p;i rib i À k dp;i p i i ¼ P; M; G; L ð13Þ