Fig. 2. Radial phylogenetic trees for selected stress proteins of four species from three super-kingdoms. Sequence comparisons were made with ClustalW (http://www.ebi.ac.uk/clustalw) and phylogenetic trees visualized using TreeView 1.6 (http://taxonomy.zoology.gla.ac.uk/rod/rod.html). Each sequence is labeled with their GenBank accession number. The length of the lines connecting individual sequences represents evolutionary distance, which is based on the degree of sequence similarity between paralogues. The examples shown illustrate that genes encoding stress proteins were subject to adaptive radiation at different times during the evolution of life, which presumably reflects their increasing role for multiple important cell functions. Other very important stress response genes such as mitogen-activated protein kinases (MAPKs) and 14-3-3 proteins display similar patterns of late adaptive radiation in eukaryotes as shown for the DNA mismatch repair factor MSH/mutS. In contrast to the latter, however, MAPKs and 14-3-3 proteins have originated in eukaryotes and are entirely absent from prokaryotes, whose phosphorylation-based signaling systems differ greatly from those in eukaryotes.