The cellular retinol binding protein II gene. Sequence analysis of the rat gene, chromosomal localization in mice and humans, and documentation of its close linkage to the cellular retinol binding protein gene.

Cellular retinol binding protein II (CRBP II) is an abundant, 134-residue protein present in the small intestinal epithelium. It is thought to participate in the uptake and/or intracellular metabolism of vitamin A. We have isolated and sequenced the rat CRBP II gene. Its four exons span 0.65 kilobases and are interrupted by three introns with an aggregate length of 19.5 kilobases. Southern blot hybridization analysis indicated that this gene is highly conserved in rats, mice, and humans. CRBP II belongs to a protein family that contains eight known members. Computer-assisted comparative sequence analyses indicated that a region of internal homology spans its first two exons and that oligopeptide domains specified by these first two exons exhibit significant homology to all other family members as well as to a portion of the all-trans-retinol binding domain that has previously been defined in serum retinol binding protein. The CRBP II gene was mapped in mice using recombinant inbred strains and restriction fragment length polymorphisms. It is located on chromosome 9 within 5.3 centimorgans of the phosphoglucomutase-3 locus and is closely linked (within 3.0 centimorgans) to the gene specifying a highly homologous intracellular retinol binding protein known as CRBP. Mouse-human somatic cell hybrids were used to determine that both the CRBP and CRBP II genes are located on human chromosome 3.