Kung S S, Wu Y M, Chow W Y
Institute of Radiation Biology, National Tsing Hua University, Taiwan, ROC.
Brain Res Mol Brain Res. 1996 Jan;35(1-2):119-30. doi: 10.1016/0169-328x(95)00193-v.
Two cDNA clones encoding putative ionotropic glutamate receptor subunits were isolated from a brain cDNA library of a freshwater fish, Oreochromis sp. The deduced amino acid sequences of these two cDNAs, fGluR2 alpha and fGluR2 beta, display the highest sequence identity (85%) to that of the rat GluR2 (AMPA receptor subunit) and they contain an arginine codon at the Q/R editing site of the TM2 segment. Genomic sequence analysis of the exons encoding the TM2 reveals the presence of an arginine codon at the Q/R site, suggesting that the RNA editing mechanism acting in the mammalian GluR2 does not operate at the homologous site in these two fish genes. In contrast to the absence of RNA editing at the Q/R site, transcripts of fGluR2 alpha and fGluR2 beta are subjected to RNA editing at a second site, the R/G site. A splicing variant of fGluR2 alpha, fGluR2 alpha-c, with a shorter C-terminal sequence was found; however, no C-terminal splicing variant of fGluR2 beta was detected in the mature fish. Similar to the mammalian AMPA receptor, variants created by the alternate choice of flip and flop modules were found among transcripts of fGluR2 alpha-c and fGluR2 beta. The amino acid sequences of flip and flop modules of fGluR2 beta are identical to that of the rat GluR2, whereas the amino acid sequences of the flip and flop modules of fGluR2 alpha-c differ from the invariant consensus sequences of the rat AMPA receptor subunits.
从淡水鱼奥利亚罗非鱼（Oreochromis sp.）的脑cDNA文库中分离出两个编码假定离子型谷氨酸受体亚基的cDNA克隆。这两个cDNA（fGluR2α和fGluR2β）推导的氨基酸序列与大鼠GluR2（AMPA受体亚基）的序列具有最高的同一性（85%），并且它们在TM2片段的Q/R编辑位点含有精氨酸密码子。对编码TM2的外显子进行基因组序列分析，发现在Q/R位点存在精氨酸密码子，这表明在哺乳动物GluR2中起作用的RNA编辑机制在这两个鱼类基因的同源位点不起作用。与Q/R位点不存在RNA编辑相反，fGluR2α和fGluR2β的转录本在第二个位点R/G位点进行RNA编辑。发现了fGluR2α的一个剪接变体fGluR2α-c，其C末端序列较短；然而，在成熟鱼中未检测到fGluR2β的C末端剪接变体。与哺乳动物AMPA受体类似，在fGluR2α-c和fGluR2β的转录本中发现了由flip和flop模块的交替选择产生的变体。fGluR2β的flip和flop模块的氨基酸序列与大鼠GluR2的相同，而fGluR2α-c的flip和flop模块的氨基酸序列与大鼠AMPA受体亚基的不变共有序列不同。
