Figure 6.

Correlated clusters of amino acids. Clusters determined by correlation analyses of amino acid composition in eukaryotes (6a) and eubacteria (6b). Amino acids with correlated frequencies are connected by lines and colored according to Pearson correlation coefficients (r): red (r > 0.8), green (0.5 <r < 0.8), and blue (0.3 <r < 0.5). It is noted that 20 alpha-amino acids group into two clusters: cluster 1 (D, F, I, K, M, N, S, T, V and Y) and cluster 2 (A, C, E, G, H, L, P, Q, R and W) for eukaryotes (6a) and cluster 1 (A, D, G, H, L, M, P, Q, R, T, V and W) and cluster 2 (C, E, F, I, K, N, S and Y) for eubacteria (6b). Amino acids in the same cluster are suggested to have common evolutionary history.