Cellular Retinoic Acid- and Cellular Retinol-Binding Proteins: Complementary Deoxyribonucleic Acid Cloning, Chromosomal Assignment, and Tissue Specific Expression

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Abstract
Both cellular retinoic acid-binding protein (CRABP) and cellular retinol-binding protein (CRBP) are widely distributed in mammalian tissues and display different patterns of tissue distribution. We have isolated cDNA clones for bovine CRABP and for human CRBP from a bovine adrenal gland cDNA library and from a human liver cDNA library, respectively, by probing with synthetic oligonucleotides. The primary structures of the two proteins inferred from the DNA sequences were identical to the previously reported amino acid sequences. The cDNA probes were used to obtain some information about the genes for CRABP and CRBP, including their chromosomal localization, and about the tissue specific expression of these two genes. Southern blot analyses under highly stringent conditions, of genomic DNA from both the bovine and the mouse, showed that for each retinoid-binding protein, specific DNA sequences are sufficiently conserved across species to allow cross-hybridization to occur. Under the same conditions, however, the DNA sequences for CRABP and CRBP within each species appear to be sufficiently different that cross-hybridization was not observed between the two cDNA probes. Using mouse-hamster somatic cell hybrids, it was demonstrated that these genes map to mouse chromosome 9 to 10. Northern blot analyses of RNA from six tissues from both the bovine and the mouse showed marked differences in the levels of the specific transcript for each binding protein among the different tissues, and in the tissue distribution of CRABP mRNA as compared to that of CRBP mRNA. In both species, CRBP mRNA was detected in more tissues than was CRABP mRNA. For both proteins, the relative tissue distribution of the mRNAs appeared to both resemble and to differ from the reported distribution of the binding proteins themselves. The factors that regulate the tissue specific expression of the genes for CRABP and CRBP remain to be determined.

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