Hospattankar A V, Higuchi K, Law S W, Meglin N, Brewer H B
Molecular Disease Branch, National Heart, Lung, and Blood Institute, Bethesda, MD 20892.
Biochem Biophys Res Commun. 1987 Oct 14;148(1):279-85. doi: 10.1016/0006-291x(87)91107-7.
Human apolipoprotein (apo) B exists in plasma as two isoproteins designated apoB-100 and apoB-48. ApoB-100 (512 kDa) and apoB-48 (250 kDa) are synthesized by the liver and intestine respectively. Analysis of apoB cDNA clones isolated from a human intestinal cDNA library revealed that the intestinal apoB mRNA contains a new in-frame translational stop codon. This premature stop codon is generated by a single base substitution of a 'C' to 'T' at nucleotide 6538 which converts the codon 'CAA' coding for the amino acid glutamine residue 2153 to an in-frame stop codon 'TAA'. The generation of a stop codon in the intestinal apoB mRNA appears to be tissue specific since it has not been reported in cDNA clones isolated from human liver cDNA libraries which code for the 4536 amino acid apoB-100. A potential polyadenylation signal sequence 'AATAAA' was also identified 390 bases downstream from the new stop codon. The new stop codon in the human intestinal apoB mRNA provides a potential mechanism for the biosynthesis of intestinal apoB-48.
人载脂蛋白（apo）B在血浆中以两种同功蛋白形式存在，分别称为apoB - 100和apoB - 48。apoB - 100（512 kDa）和apoB - 48（250 kDa）分别由肝脏和肠道合成。对从人肠道cDNA文库中分离出的apoB cDNA克隆进行分析发现，肠道apoB mRNA含有一个新的框内翻译终止密码子。这个提前出现的终止密码子是由核苷酸6538处的一个碱基“C”替换为“T”产生的，它将编码谷氨酰胺残基2153的密码子“CAA”转换为一个框内终止密码子“TAA”。肠道apoB mRNA中终止密码子的产生似乎具有组织特异性，因为在从人肝脏cDNA文库中分离出的编码4536个氨基酸的apoB - 100的cDNA克隆中尚未有相关报道。在新的终止密码子下游390个碱基处还鉴定出一个潜在的聚腺苷酸化信号序列“AATAAA”。人肠道apoB mRNA中的新终止密码子为肠道apoB - 48的生物合成提供了一种潜在机制。
