The human apoB-100 gene: ApoB-100 is encoded by a single copy gene in the human genome

Northern blot analysis of human liver and intestine mRNA revealed two separate apoB mRNA of 14.1 and 7.5 kb in the intestine, and a single 14.1 kb apoB mRNA in the liver. cDNA probes which encode for the 5′, middle, and 3′ regions of the human apoB-100 mRNA have been utilized to evaluate the number of apoB genes present in the human genome by Southern blot hybridization analysis. Comparison of restriction enzyme digestions of high molecular weight leukocyte DNA and a known apoB genomic clone with cDNA probes for the 5′, middle and 3′ regions of the apoB-100 mRNA were consistent with only a single apoB gene per human haploid genome. Further analysis with synthetic oligonucleotides definitively established that there is a single apoB-100 gene. The two mRNA species observed in the intestine must be derived from a single nuclear apoB RNA transcript.