Cloning of genomic and cDNA sequences encoding an invertebrate γ-aminobutyric acidA receptor subunit

Abstract

system poly(A)' RNA, when probed with a genomic fragment encoding part of transmembrane domain M2 and all of M3. This indicates that only a very low level of the putative GABA, receptor @-subunit transcripts are present in the adult molluscan central nervous system. The highly sensitive technique of PCR [9] has been used to amplify an approximately 400 bp portion of both GABA, receptor /?-subunit mRNAs that encode part of the extracellular domain and transmembrane domains M1, M2 and M3. DNA sequencing of the PCR products has confirmed that both genes are expressed and that the introns predicted from the gene sequence are spliced out correctly. A comparison of the deduced amino-acid sequence of one of the cDNAs with the bovine pl-subunit sequence [8] is shown in Fig. 1. Note the high degree of conservation of the sequence between the mammal and the mollusc, and that this is highest of all in the transmembrane domains. Interestingly, one intron was found within the M2 transmembrane domain; this is in direct contrast with studies on other ligand-gated ion-channel subunit genes in which