Fig. 4.

Proline Usage Remains Stable Over Time Across Clades—AGA (Arg) Consistently Overrepresented in ORF1ab, Spike and N Genes. Line graphs highlight the average relative synonymous codon usage (RSCU) of the four proline codons (CCA (blue), CCC (orange), CCG (green), and CCT (red)). Heatmaps show the average RSCU per codon (y-axis) for four months spanning each clades largest sampling months (bolded regions of Table 1). A codon with a RSCU value of > 1.5 is considered highly overrepresented and < 0.5 is considered highly underrepresented. Black boxes represent a missing codon. A ORF1ab gene proline average RSCU over time. B ORF1ab gene average RSCU for all codons. C Spike gene proline average RSCU over time. D Spike gene average RSCU for all codons. E N gene proline average RSCU over time. F N gene average RSCU for all codons. All line graphs utilized the bold regions of the Table 1 clade distributions