Heterotrimeric guanine nucleotide-binding proteins (G proteins) integrate signals between receptors and effector proteins. They are composed of an alpha, a beta, and a gamma subunit. The product of the human guanine nucleotide-binding protein beta-3 subunit gene is a modulator or transducer in various transmembrane signaling systems and integrates signals between receptors and effector proteins. To date, the human G-protein beta 3 subunit (GNB3) gene and some of its variants represent some of the best examples of genetic influences that are involved in the determination of hypertension and obesity, which make it a sensible candidate gene for type 2 diabetes.

The heterotrimeric guanine nucleotide-binding protein subunits are encoded by families of related genes. The human guanine nucleotide-binding protein beta-3 subunit gene encodes a 34 kd beta subunit. Beta subunits are expressed in all tissues and are important regulators of alpha subunits, as well as of certain signal transduction receptors and effectors. A single-nucleotide polymorphism (C825T) in this gene is associated with essential hypertension and obesity. This polymorphism is also associated with the occurrence of the splice variant GNB3-s, which appears to have increased activity. GNB3-s is an example of alternative splicing caused by a nucleotide change outside of the splice donor and acceptor sites. Additional splice variants may exist for this gene, but they have not been fully described.