FIGURE 1.

Phylogenetic distribution of known PPTKs. Alignment of the kinase domains of known PPTKs revealed clustering into three main families of tyrosine kinases: the BY-kinases (BYK), the Hanks-type PPTKs (HYK), and the “odd” PPTKs (OYK). The BY-kinases further clustered according to their architectural subtypes: the single-protein P-type and the two-protein F-type. The Hanks-type PPTKs clustered together with the eukaryotic kinases (Src tyrosine kinase and Ser/Thr cAMP-dependent protein kinase A) and the Hanks-type Ser/Thr kinase PknB of M. tuberculosis. The DivL kinase of C. crescentus and the putative BC4770 tyrosine kinase of B. cereus clustered with the histidine kinases of E. coli (EnvZ and PhoR). P. aeruginosa WaaP is reported to contain 9 of the 11 Hanks domains (51) and clustered near the Hanks-type PPTKs. Although grouped together, the “odd” PPTKs are distantly related as expected. The following sequences were used for alignment in ClustalX2: the C-terminal catalytic domains of BY-kinases; the kinase domains of Hanks-type kinases and histidine/histidine-like kinases, identified using the ScanProsite tool (70); the catalytic domain of M. tuberculosis PtkA determined in Fig. 3; and full-length PutA and WaaP as their tyrosine kinase domains are not defined. The phylogenetic tree was displayed using Molecular Evolutionary Genetics Analysis (MEGA) 5 software.