A partial cDNA clone for human apolipoprotein B.

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Abstract
A human liver cDNA library was screened for sequences coding for apolipoprotein B (apo B), the major protein of human low density lipoproteins. A mixture of synthetic oligonucleotides (26 bases long) coding for an amino acid sequence known to exist in apo B was used as a hybridization probe. A clone was identified that had a cDNA insert of 593 base pairs and that contained sequences coding for a peptide of 24 residues that had earlier been isolated from apo B by limited proteolysis. The entire nucleotide sequence of the cDNA insert consists of 1 open reading frame coding for 197 amino acids. Apo B-related RNAs were found in human liver, baboon liver, and the human hepatoma cell line HepG2. None were detected in placenta, simian virus 40 (SV40)-transformed fibroblasts, and a lymphoblastoid cell line. The length of the mature apo B mRNA was estimated to be 18kb [kilobases], enough to code for a protein with a MW in the neighborhood of 500,000.