 Lefkowitz studies receptor biology and signal transduction and is most well known for his detailed characterizations of the sequence, structure and function of the β-adrenergic and related receptors and for the discovery and characterization of the two families of proteins which regulate them, the G protein-coupled receptor (GPCR) kinases and β-arrestins.Lefkowitz made a remarkable contribution in the mid-1980s when he and his colleagues cloned the gene first for the β-adrenergic receptor, and then rapidly thereafter, for a total of 8 adrenergic receptors (receptors for adrenaline and noradrenaline).This led to the seminal discovery that all GPCRs (which include the β-adrenergic receptor) have a very similar molecular structure.