By sequencing clones obtained from a size-fractionated brain cDNA library, Nagase et al. (1998) cloned MAST3, which they designated KIAA0561. The transcript contains repetitive elements in its 3-prime UTR, and the deduced 1,308-amino acid protein shares significant similarity with mouse Mast205 (MAST2) and human MAST4. RT-PCR detected variable MAST3 expression in all tissues examined, with highest levels in kidney, brain, and small intestine.Valiente et al. (2005) showed that the C-terminal tail of human PTEN bound to the PDZ domains of rat Magi2, Magi3, and Dlg (DLG1), mouse Sast (MAST1) and Mast205, and human MAST3. Interaction of PTEN with Magi2 increased PTEN protein stability, and interaction of PTEN with the MAST kinases facilitated phosphorylation of PTEN by these kinases.