[Gene families of G protein subunits]

G proteins are heterotrimers composed of alpha, beta, and gamma subunits. So far 16 alpha, 6 beta, and 12 gamma subunit genes have been described in mammals. G protein subunit gene families are comparatively conservative and primitive, with all of which exon-intron junctions conform to the GT-AG rule except for one alternative splice site at 5'-end of exon 4 in Gnas which uses GT-TG junction. In the coding regions, exon-intron structures and intron positions among each of the subunit gene families are comparatively conserved. Most of the G protein genes have some characteristics of housekeeping genes. Analysis of distribution of G protein subunit genes in mammalian genomes reveals a tendency of clustering, with five pairs of the alpha subunit genes arranging as tandem duos.