Functional classification of conserved phosphosites. (a) Main classes. The height of the bars represents the percentage of phosphosites with homologs in a specific number of different species (indicated by the color of the bar) belonging to the different classes. The black arrows indicate groups with homologs in a specific number of species that are significantly over-represented (arrows pointing up) or under-represented (arrows pointing down) compared with all phosphorylation events in that functional category. Significance was determined using a Fisher's exact test; scores with a P value below 0.05 after Bonferroni correction were considered significant. (b) Subclasses. The numbers in the cells are the fold increase of the fraction of phosphosites in that subclass relative to the fraction in that subclass of phosphosites without homologs in other species (2log [sites in n species] - 2log [sites in 1 species]). Over-representation is presented in red, and under-representation in blue. Only classes with a total of 80 or more sites and with at least one site found in a total of four species are shown. The black boxes indicate significant under-representation or over-representation (Fisher's exact test, P < 0.05 after Bonferroni correction).