Sánchez Joaquín
Facultad de Medicina, UAEM, Av. Universidad 1001, Col. Chamilpa, Cuernavaca 62100, Morelos, Mexico.
Biochem Biophys Res Commun. 2008 Sep 5;373(4):589-92. doi: 10.1016/j.bbrc.2008.06.076. Epub 2008 Jun 27.
The occurrence of a main amino acid at the start of proteins from various vertebrate species is reported. Computer analyses of protein-coding sequences showed that alanine occurs in one out of five cases as the second amino acid in proteins from seven mammals (including man), one amphibian, one bird and two fishes. We also show that the alanine codon GCG occurs >3-fold more often as second codon than in general, i.e. GCG was overrepresented. Options to explain the abundance of alanine as second amino acid may already exist, but the overrepresentation of GCG was harder to explain because GCG was classically a rare codon. However, based on similarities with the published translation-initiation enhancer sequence CCGGCGG, which has complementarity with 18S ribosomal RNA, a theoretical role of GCG in translation initiation is suggested. Namely, GCG is proposed to be part of a sequence with potential for base-pairing with 18S ribosomal RNA.
据报道，在各种脊椎动物物种的蛋白质起始位置存在一种主要氨基酸。对蛋白质编码序列的计算机分析表明，在七种哺乳动物（包括人类）、一种两栖动物、一种鸟类和两种鱼类的蛋白质中，每五个案例中就有一个案例的第二个氨基酸是丙氨酸。我们还表明，丙氨酸密码子GCG作为第二个密码子出现的频率比一般情况高出三倍多，即GCG出现频率过高。解释丙氨酸作为第二个氨基酸丰度的原因可能已经存在，但GCG出现频率过高则更难解释，因为传统上GCG是一个稀有密码子。然而，基于与已发表的翻译起始增强子序列CCGGCGG的相似性，该序列与18S核糖体RNA具有互补性，因此推测了GCG在翻译起始中的理论作用。也就是说，GCG被认为是一个有可能与18S核糖体RNA进行碱基配对的序列的一部分。
