Detailed sequence analysis of the kinase domains of GiPI3K1 and GiPI3K2. Multiple sequence alignment of the kinase domains of the giardial PI3Ks with a structurally characterised Class I PI3K-kinase domain from Sus scrofa, Ss PI3Kγ, [GenPept: NP_999104] demonstrates conservation of functional residues. Sequences were aligned using ClustalW . Arrows indicate the boundary between the N- and C-terminal lobes of the kinase domain for the S. scrofa sequence. Insertions in the kinase domains of GiPI3K1 and GiPI3K2 are shown in boxes (not to scale). Solid underlined residues indicate activation loop residues in the S. scrofa sequence essential for substrate specificity. Dashed underlined residues indicate catalytic loop residues in the S. scrofa sequence. Key: ◇, ATP binding residues; ▲, PI-binding residues; ○, metal binding residues; □, possible substrate-activating base/nucleophile to attack γ-phosphate of ATP.