Structure of the Bovine Natural Resistance Associated Macrophage Protein (NRAMP 1) Gene and Identification of a Novel Polymorphism

The NRAMP 1 gene is a major candidate gene influencing the outcome of infections with intracellular pathogens in numerous species. NRAMP 1 is highly conserved in many mammalian species and the NRAMP 1 gene shows considerable conservation in structure between mice and humans. The association of NRAMP 1 gene polymorphisms with disease in cattle has been limited to a single microsatellite located within the 3'-non coding region of the bovine NRAMP 1 gene. In order to facilitate further studies on this important gene, we now report the nearly complete structure of the bovine NRAMP 1 gene, including sizes and positions of 13 introns relative to the bovine NRAMP 1 gene coding sequence and the DNA sequence of intron-exon junctions. Comparison of the bovine, murine and human NRAMP 1 gene structures revealed a high degree of conservation in intron placement, though the lengths of several introns were less-well conserved. In general, the greatest divergence in intron lengths occurred in regions of the NRAMP 1 gene displaying the lowest coding sequence conservation. In addition, mutations near intron-exon junctions could account for 25 of the 75 total amino acid differences between murine and bovine NRAMP 1. Using information gained through this study, it was possible to rapidly identify a novel polymorphism within the bovine NRAMP 1 gene intron X. This polymorphism was shown by direct DNA sequence analysis to consist of insertion of three guanine nucleotides at positions 37,40 and 98 relative to the intron X start point. Initial scans of several cattle breeds suggest that the two intron X alleles identified here are stable and widespread in the Bos taurus population.