Natural resistance to infection with unrelated intracellular parasites such as Mycobacteria, Salmonella, and Leishmania is controlled in the mouse by a single gene on chromosome 1, designated Bcg, Ity, or Lsh. A candidate gene for Bcg, designated natural resistance-associated macrophage protein (Nramp), has been isolated and shown to encode a novel macrophage-specific membrane protein, which is altered in susceptible animals. We have cloned and characterized cDNA clones corresponding to the human NRAMP gene. Nucleotide and predicted amino acid sequence analyses indicate that the human NRAMP polypeptide encodes a 550-amino acid residue membrane protein with 10-12 putative transmembrane domains, two N-linked glycosylation sites, and an evolutionary conserved consensus transport motif. Identification of genomic clones corresponding to human NRAMP indicates that the gene maps to chromosome 2q35 within a group of syntenic loci conserved with proximal mouse 1. The gene is composed of at least 15 exons, with several exons encoding discrete predicted structural domains of the protein. These studies have also identified an alternatively spliced exon encoded by an Alu element present within intron 4. Although this novel exon was found expressed in vivo, it would introduce a termination codon in the downstream exon V, resulting in a severely truncated protein. Northern blot analyses indicate that NRAMP mRNA expression is tightly controlled in a tissue-specific fashion, with the highest sites of expression being peripheral blood leukocytes, lungs, and spleen. Additional RNA expression studies in cultured cells identified the macrophage as a site of expression of human NRAMP and indicated that increased expression was correlated with an advanced state of differentiation of this lineage.

The mouse gene locus Lsh/Ity/Bcg regulates macrophage activation for antimicrobial activity against intracellular pathogens. A candidate gene, designated natural resistance-associated macrophage protein gene (Nramp), recently isolated from a mouse pre-B cell cDNA library, encodes an integral membrane protein that has structural homology with known prokaryotic and eukaryotic transport systems. In the present study, the cDNA for human Nramp was isolated by screening a human monocyte cDNA library. The cDNA was 2245 bp in length and coded for a protein of 483 amino acid residues with a molecular weight mass of 52.8 kDa. The deduced amino acid sequence was 89% homologous with that of mouse. Southern blot analysis indicated a single gene for Nramp counterpart in the human genome. Northern blot analysis revealed a single species of mRNA of approximately 2.5 kb.

>P49279|NRAM1_HUMAN Natural resistance-associated macrophage protein 1 - Homo sapiens (Human).
MTGDKGPQRLSGSSYGSISSPTSPTSPGPQQAPPRETYLSEKIPIPDTKPGTFSLRKLWAFTGPGFLMSIAFLDPGNIES
DLQAGAVAGFKLLWVLLWATVLGLLCQRLAARLGVVTGKDLGEVCHLYYPKVPRTVLWLTIELAIVGSDMQEVIGTAIAF
NLLSAGRIPLWGGVLITIVDTFFFLFLDNYGLRKLEAFFGLLITIMALTFGYEYVVARPEQGALLRGLFLPSCPGCGHPE
LLQAVGIVGAIIMPHNIYLHSALVKSREIDRARRADIREANMYFLIEATIALSVSFIINLFVMAVFGQAFYQKTNQAAFN
ICANSSLHDYAKIFPMNNATVAVDIYQGGVILGCLFGPAALYIWAIGLLAAGQSSTMTGTYAGQFVMEGFLRLRWSRFAR
VLLTRSCAILPTVLVAVFRDLRDLSGLNDLLNVLQSLLLPFAVLPILTFTSMPTLMQEFANGLLNKVVTSSIMVLVCAIN
LYFVVSYLPSLPHPAYFGLAALLAAAYLGLSTYLVWTCCLAHGATFLAHSSHHHFLYGLLEEDQKGETSG