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

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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.