Molecular Analysis of cDNA Molecules Encoding Glutamate Receptor Subunits,fGluR1α and fGluR1β,of Oreochromis sp.

Abstract

In this study, we isolated two cDNA molecules encoding putative glutamate receptor subunits, fGluR1α and fGluR1β, from an Oreochromis sp. brain cDNA library by hybridizing with the glutamate receptor cDNA, fGluR2β, of the same fish. The deduced amino acid sequence of the fGluR1α consists of 908 residues with an 18-residue signal peptide and displays a sequence identity of 74% to the amino acid sequence of rat GluR1 subunit. Northern blotting indicates that the expression level of fGluR1α in telencephalon is higher than that in optic tectum and cerebellum in adult fish brain. Reverse-transcriptase polymerase chain reaction and genomic analyses reveal the presence of variants created by alternative splicing at the flip-flop module and the carboxyl terminus of fGluR1α transcripts. The amino acid sequence of fGluR1α is unique in that it contains a glutamine-rich sequence inserted at the loop 1 (L1) between transmembrane domains 1 and 2. A second incomplete cDNA clone, designated fGluR1β, coding for a polypeptide showing sequence identity to the rat GluR1 and fGluR1α was isolated from the same library. Insertion of a serine- and glutamine-rich sequence at the L1 was also detected in the translated sequence of fGluR1β.