Transcription. The viral polymerase on the leader region of the genome starts either transcription or replication. If there are sufficient N proteins, transcription is inhibited by the encapsidation of nascent positive-sense RNAs by N proteins; then replication dominates transcription [41, 52, 53] . In contrast, if there are insufficient free N proteins, then transcription dominates replication. In the model we correlate the extent of transcription dominance with the availability of N proteins by introducing a factor, encap. This factor is defined as the ratio of the number of free N proteins to the number required to encapsidate all available nascent genome-sized viral RNAs. Only nocap (¼ 1 À encap) of the polymerases bound to the genomic promoters can start the transcription: dpol N;1 dt ¼ k e;pol ðð1 À / N Þ nocap pol l l l À n sec;N l mRNA;N pol N;1 Þ ð 7Þ