Nakasaki Y, Iwamoto T, Hanada H, Imagawa T, Shigekawa M
Department of Molecular Physiology, National Cardiovascular Center Research Institute, Osaka.
J Biochem. 1993 Oct;114(4):528-34. doi: 10.1093/oxfordjournals.jbchem.a124211.
The amino acid sequences of two isoforms of the rat aortic smooth muscle Na+/Ca2+ exchanger have been deduced by cloning and sequencing the cDNAs. These isoforms are identical in nucleotide sequence except that one has a 23-amino acid insertion at amino acid position 570. They are highly homologous to the canine cardiac exchanger except for the NH2-terminal portion and part of the large central hydrophilic domain (amino acid residues 570-631). They are 902 and 925 (with the insertion) amino acid long with calculated molecular masses of 100,676 and 103,200 (with the insertion), respectively, if the NH2-terminal 32-amino acid residues are eliminated as a cleaved signal sequence. Amplification of the variable region (amino acids 570-631) of the exchanger by means of the reverse transcriptase-polymerase chain reaction and DNA sequencing revealed that many isoforms of the exchanger are expressed in different rat tissues. The two clones isolated in this study are the predominant isoforms expressed in aorta, stomach, liver, and kidney. In cardiac and skeletal muscles, another isoform is dominant, which is equivalent to the canine cardiac exchanger. In brain, a third type is predominantly expressed. Alignment of the nucleotide sequences of these isoforms and Southern blot analysis of rat genomic DNA suggested that each isoform is generated through alternative splicing of the primary transcript.
通过对大鼠主动脉平滑肌钠钙交换蛋白的cDNA进行克隆和测序，推导得到了该蛋白两种同工型的氨基酸序列。这两种同工型的核苷酸序列相同，只是其中一种在氨基酸位置570处有一个23个氨基酸的插入片段。除了氨基末端部分和大的中央亲水区的一部分（氨基酸残基570 - 631）外，它们与犬心脏钠钙交换蛋白高度同源。如果将氨基末端的32个氨基酸残基作为切割信号序列去除，它们分别由902和925个氨基酸（含插入片段）组成，计算得到的分子量分别为100,676和103,200（含插入片段）。通过逆转录聚合酶链反应和DNA测序对钠钙交换蛋白可变区（氨基酸570 - 631）进行扩增，结果显示该交换蛋白的多种同工型在大鼠不同组织中表达。本研究中分离得到的两个克隆是在主动脉、胃、肝脏和肾脏中表达的主要同工型。在心肌和骨骼肌中，另一种同工型占主导，它等同于犬心脏钠钙交换蛋白。在大脑中，主要表达第三种类型。这些同工型核苷酸序列的比对以及大鼠基因组DNA的Southern印迹分析表明，每种同工型是通过初级转录本的可变剪接产生的。
