Fig. 6.

Separate evolutionary origins of the co-occurrence of modifiable residues at positions 218 and 222 of eIF2α. The combined character states were encoded with colors as follows. Blue (state 1: (0,0)); yellow (state 2: (0,1)); green (state 3: (1,0)); red (state 4: (1,1)). Those pairs of species that differed in both characters and were phylogenetically separate (the path between them along the branches of the tree do not touch the path of any other pair) are shown connected by a thick orange line. Since we are examining pairs contrasting in both characters, there are two types of possible pairs: a pair is considered to be positive when the presence of a phosphorylatable residue in a member of the pair is accompanied by a methionine in the same member of the pair {red, blue}, otherwise the pair is referred to as negative {yellow, green}. In addition, to show that the co-occurrence of both PTMs has multiple and independent evolutionary origins, it can also be noted that the number of positive pairs is greater than the number of negative pairs