ative MedChemExpress Digitoxin kinase sequences, matching 4294 significant PFAM domains, which makes an average of 1.4 domains per kinase. According to PFAM, 3292 domains have kinase catalytic activity and the remaining 1002 have nonkinase domain activity. This suggests that the kinase proteins have an enormous richness of functional domains, with an average 0.3 of non-kinase domains and 1.1 kinase domains per sequence. We find that there are a total of 72 different domain types, of which 7 are annotated in PFAM to have kinase activity: Pkinase, Pkinase_C, PI3_PI4_kinase, BCDHK_Adom3, RIO1, Pkinase_Tyr and Alpha_kinase. The Pkinase domain is the most common type of kinase domain in our fungi, where it represents about 87% of all catalytic domains, and in PFAM, with more than 
32000 representative sequences. But Pkinase is not the only conserved kinase catalytic domain type. There are 425 additional putative kinases with a catalytic kinase domain different from the classical kinase catalytic domain Pkinase: Pkinase_C is a kinase C terminal domain, PI3_PI4_kinase is a phosphatidylinositol 3- and 4-kinase domain, BCDHK_Adom3 is a mitochondrial dehydrogenase kinase domain, RIO1 is a typical serine kinase domain, the Pkinase_Tyr kinase, a tyrosine kinase domain and Alpha_kinase an alpha kinase domain. These functional domains have very broad and general functions, thus explaining why they appear in all types of fungi and also in the human kinome. The exception is BCDHK_Adom3; this domain is involved in the regulation of the dehydrogenase complex that breaks down branched-chain amino-acids and it is similar to the HATPase_c family. Interestingly, however, these are, as mentioned, the 10 most common accessory domains PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/1979435 in fungi, while in human only two of them, Pkinase_C and C1_1, are also among the 10 most common domains. The remaining six domains that do exist in the human kinome are far less common than in fungi, indicating that these kinase associated domains could be good indicator of functional differences among species. We believe that the kinome domain distribution, both in type and number, should be indicative of functional and evolutionary differences between fungi. In the next section, we show that this variability is enough to differentiate among different fungal phyla and subphyla. Domain analysis and Principal Component Analysis grouping Taxonomic classification is not always a straightforward task. In this work we tested several criteria for clustering all 30 fungi studied here, based on the number and type of kinases and additional domains. Following that, we compared the results with fungal taxonomy. Four species fall outside these clusters. Of those, two do not reside in any group, and two are mixed: among the ascomycetes, one member of the Pezizomycota and one member of the Saccharomycotina crossed to the other side of the cluster boundaries. Very interestingly, here again S. pombe, clusters differently from the Pezizomycotina and Saccharomycotina groups. Indeed, when looking closely at the domain content, there are several examples in which S. pombe is quite different from its ascomycete relatives. For example, it has a much lower density of HATPase_c domains, a higher percentage of HEAT domains and a higher percentage of the Rapamycin_bind domains. It would be difficult to conclude whether this reflects any aspect of fission yeast lifestyle, or is simply a consequence of evolutionary distance among the species. The PCA results indicate clearly that