Molecular Cloning of Human Apolipoprotein E Variant Gene:E5 and E7

载脂蛋白E（apoE）是人血清脂蛋白中的一种蛋白质，用等电聚焦技术检测到apoE的三种主要亚型apoE 2、apoE 3和apoE 4以及次要亚型apoE 1、apoE 5和apoE 7。本研究克隆了一个与高脂血症和糖尿病相关的apoE 3/E7表型个体的apoE 7基因和一个与轻度高脂血症相关的apoE 2/E5表型个体的apoE 5基因，并对apoE 7等位基因的112、145和158位分别编码半胱氨酸、精氨酸和精氨酸进行了DNA序列分析。然而，在正常apoE 3同功蛋白的244和245位，观察到编码两个赖氨酸密码子而不是两个谷氨酸密码子的双碱基替换（GA）。这两个连续的氨基酸取代在突变的apoE 7同工蛋白中产生赖氨酸簇（-lys-leu-lys-lys-），这可能导致脂蛋白代谢缺陷。ApoE 5等位基因分别在位置112、145和158编码半胱氨酸、精氨酸和精氨酸。此外，该等位基因在成熟apoE的NH_2端附近的第3位氨基酸残基上有一个碱基替换（GA），即赖氨酸替换为谷氨酸。因此，该等位基因是一种新的变异体，aopE 5等位基因。

Apolipoprotein E (apoE) is one of the protein moieties of the human serum lipoproteins, Three major isoforms of apoE (apoE2, aopE3 and aopE4) and minor isoforms (apoE1, apoE5 and apoE7) have been detected by isoelectric focusing. In this study we have cloned the apoE7 gene from a subject with the apoe3/E7 phenotype associated with hypertriglyceridemia and diabetes mellitus and apoE5 gene from a subject with the apoE2/E5 phenotype associated with mild hypertriglyceridemia.DNA sequence analysis of the apoE7 allele encoded for cysteine, arginine and arginine at positions 112, 145 and 158, respectively. However, double base substitutions (G A) that coded for two lysine codons instead of the two codons for glutamic acid, at the positions 244 and 245 of the normal apoE3 isoprotein, were observed. These two continuous amino acid substitutions create a lysine cluster (-lys-leu-lys-lys-) in the mutated apoE7 isoprotein and this may result in defective lipoprotein metabolism.ApoE5 allele encodes for cysteine, arginine, and argine at positions 112, 145 and 158, respectively. In addition, this allele has a base substitution (G A) which causes the substitution of lysine for glutamic acid at residue 3 near the NH_2-terminus of the matured apoE. This allele is therefore a new nariant, the aopE5 allele.