Identification and characterization of a second mouse Nramp gene.

The Nramp gene was isolated as a candidate for the host resistance locus Bcg/Ity/Lsh, which controls natural resistance of mice to several types of infections. We have isolated by cross-hybridization cDNA clones corresponding to a second mouse Nramp gene, which we designate Nramp2. Nucleotide and predicted amino acid sequence analyses of full-length cDNA clones for Nramp2 indicate that this novel Nramp protein is closely homologous to the previously described Nramp and that the two genes form part of a small gene family. The two Nramp proteins encode integral membrane proteins that share 63% identical residues and an overall homology of 78%. They share very similar secondary structure, including identical hydropathy profiles and predicted membrane organization, with a minimum of 10 and most probably 12 transmembrane domains, a cluster of predicted N-linked glycosylation sites, and a consensus transport motif. Analysis of the distribution of Nramp2 mRNA transcripts in normal mouse tissues by Northern blotting revealed that the Nramp2 gene produces several mRNAs, including prominent 3.3- and 2.3-kb species generated by the use of alternative polyadenylation signals. In contrast to the previously described macrophage-specific Nramp gene, Nramp2 mRNAs were found to be expressed at low levels in all tissues tested. Using a polymorphic (GT)26 dinucleotide repeat identified in the 3' untranslated region of the mRNA, we have mapped the Nramp2 gene to the distal part of mouse chromosome 15 between markers D15Mit41 and D15Mit15, with the gene order and intergene distance (in cM): centromere-56.1-D15Mit41-(1 +/- 1)-Nramp2-(5 +/- 2)-D15Mit15.