ALTERNATIVE SPLICING OF A 51-NUCLEOTIDE EXON THAT ENCODES A PUTATIVE PROTEIN-KINASE-C PHOSPHORYLATION SITE GENERATES 2 FORMS OF THE CHICKENGAMMA-AMINOBUTYRIC ACID(A) RECEPTOR BETA-2 SUBUNIT

Complementary DNAs that encode two forms of the chicken gamma-aminobut yric acid type A (GABA(A)) receptor beta 2 subunit have been isolated. These polypeptides differ by the presence (beta 2L) or absence (beta 2S) of 17 amino acids, which contain a possible target for phosphoryla tion by protein kinase C, in the large intracellular loop between the third and fourth membrane-spanning domains. The extra sequence in the chicken beta 2L subunit is not found in previously published GABA(A) r eceptor beta 2-subunit sequences. Analysis of genomic DNA has revespli cing of a novel 51-nucleotide exon. Although the two beta 2-subunit tr anscripts appear to be present in 1-day-old chick brain at similar ste ady-state levels, we have been unable to detect an mRNA for the long f orm of the beta 2 subunit in either the bovine or the rat. Because the various GABA(A) receptor genes are thought to have arisen by duplicat ion ofancestor, our data, taken together with that on the gamma 2 subu nit, which occurs in two forms that arise by alternative splicing of a 24-nucleotide exon, suggest that the coding region of the primordial gene or one of its very early descendants contained 10 exons, not nine as previously thought.