STRUCTURE OF THE HEPATIC CONTROL REGION OF THE HUMAN APOLIPOPROTEIN-EC-I GENE LOCUS/

The specificity of expression in the liver of the human apolipoprotein (ape) E/C-I gene locus is determined by a hepatic control region (HCR ) that is located 15 kilobases downstream of the apoE gene, DNase I fo otprint studies of this sequence using nuclear extracts identified a r egion of the HCR that is enriched in nuclear protein-binding sites. Nu clease analysis of chromatin revealed liver-specific DNase I-hypersens itive sites that were associated with this region, and additional live r-specific nuclease-sensitive sites associated with the apoE gene were identified, The HCR domain has a limited binding affinity for the nuc lear scaffold, The specific domain required for liver expression was t ested by ligating subfragments of the HCR to the apoE gene and examini ng their activity in transgenic mice, A segment of 319 nucleotides tha t contained several potential regulatory sequences was required for fu ll activity of liver-specific transcription with shorter segments yiel ding much lower levels of expression in the liver. All constructs that contained a fully active HCR were expressed in approximately a copy-d ependent manner, suggesting that transgene expression was independent of integration position. Taken together, the properties of the HCR are consistent with its function as a locus control region for the liver- specific expression of the apoE gene.