Mapping of the beta 2 subunit gene (GABRB2) to microdissected human chromosome 5q34-q35 defines a gene cluster for the most abundant GABAA receptor isoform.

The gamma-aminobutyric acid receptor (GABAAR) is a multisubunit Cl- channel that mediates most fast inhibitory synaptic transmission in the central nervous system. Molecular evolution has given rise to many genetic variants of GABAAR subunits, including alpha 1-6, beta 1-4, gamma 1-4, delta, and rho 1-2, suggesting that an enormous number of combinations of subunits are possible. Here we report that the beta 2 gene is located on chromosome 5q34-q35, defining a cluster comprising alpha 1, beta 2, and gamma 2 genes that together code for the most abundant GABAAR isoform. The fact that intron position is conserved in the beta 1-3 genes, taken together with the observation that chromosomes 4 and 15 also contain distinct alpha-beta-gamma gene clusters, strongly suggests that an ancestral alpha-beta-gamma cluster was duplicated and translocated to at least two different chromosomes. This organization of GABAAR gene clusters may have been preserved as linkage provides a mechanism for facilitating coordinate gene expression.