Protein kinase B (PKB) is a major downstream target of receptor tyrosine kinases that signal via phosphatidylinositol 3-kinase PIK3). Upon cell stimulation, PKB is translocated to the plasma membrane, where it is phosphorylated on thr308 in the catalytic domain and ser473 in the C-terminal regulatory domain. Several protein partners for PKB have been identified. CTMP, a carboxyl terminal modulator protein, binds to PKB and negatively regulates PKB activity by inhibiting phosphorylation of these PKB residues. CTMP (mouse 248aa, human 240aa, chromosome 1q21, 22-26kD) predominantly expressed in skeletal muscle, testis, uterus, brain, and kidney, with lower levels in heart, liver, and lung. The presence of multiple transcripts suggested that CTMP undergoes alternative splicing.