The human high affinity IgE receptor (FceRI) is a central component of the allergic response and is expressed as either a trimeric a2 or tetrameric aß2 complex. It has been previously described that the cytoplasmic domain (CD) of the a-chain carries a dilysine motif at positions -3/-7 from the C-terminus that functions in intracellular retention prior to assembly with other FceRI subunits. In this report we have further explored the role of the -3/-7 dilysine signal in controlling steady state a-chain transport by mutational analysis and found little surface expression of a -3/-7 dialanine a-chain mutant but significant Golgi localization. We compared the transport properties of a series of a-chain CD truncation mutants and observed that truncation mutants lacking 23 or more C-terminal residues showed a dramatic increase in steady state transport suggesting a role for the membrane-proximal CD sequence in a-chain retention. By performing alanine-scanning mutagenesis we identified a dilysine sequence (K212K216) proximal to the transmembrane domain (TMD) that is important for both a-chain cell surface expression and intracellular stability. Furthermore, co-mutation of the K212K216 residues with the -3/-7 dilysine signal produced a dramatic increase in a-chain surface expression that was further increased by co-mutation of the lone charged residue (D192) in the TMD thereby defining three regions that function to regulate a-chain transport and in a highly synergistic manner.