Organization, sequence and nuclease hypersensitivity of repetitive elements flanking the chicken apoVLDLII gene: extended sequence similarity to elements flanking the chicken vitellogenin gene.

Analysis of nuclease hypersensitivity of regions flanking the estrogen-dependent, chicken apoVLDLII gene has revealed an hepatic, DNaseI hypersensitive site whose sensitivity is influenced by both the developmental stage and sex of the bird. The site is located 3.0kb upstream from the gene, in a block of middle repetitive elements. Contact hybridization studies indicate that the block consists of contiguous copies of two elements with reiteration frequencies of 500-1000 and 10,000-30,000 copies per haploid genome. Sequencing of 1.8kb spanning the repeats has revealed that the higher frequency element is a member of the CR1 family. The adjacent lower frequency repeat can also be found next to another member of the CR1 family located in the 3' flanking region of the vitellogenin gene. The hypersensitive site has been mapped to one of the two most highly conserved regions of the CR1 element. This region displays homology with a silencer sequence recently identified in a CR1 element flanking the chicken lysozyme gene.