Structural organization, sequence, and expression of the chicken NRAMP1 gene encoding the natural...

One of the most common causes of food poisoning in humans is salmonellosis, which is frequently caused by ingestion with Salmonella-contaminated poultry products. Several lines of evidence suggest that genetic factors control resistance and susceptibility of chickens to infection with Salmonellae. In the mouse, innate resistance to infection with intracellular pathogens such as Salmonella typhimurium, several species of Mycobacteria, and Leishmania donovani is controlled by the mouse chromosome 1 Nramp1Bcg gene. To investigate the role of NRAMP1 in the differential resistance and susceptibility of chickens to infections with S. typhimurium, we have cloned and characterized cDNA clones corresponding to the chicken NRAMP1 gene. Nucleotide and predicted amino acid sequence analyses indicate that the chicken NRAMP1 polypeptide encodes a 555-amino-acid residue membrane protein with 12 putative transmembrane domains, two N-linked glycosylation sites, and an evolutionary conserved consensus transport motif. The peptide sequence identity among chicken, mouse, and human NRAMP1 is 68%. The chicken NRAMP1 gene contains 15 exons and spans 5 kb of genomic DNA. One major and two minor transcription initiation sites were detected using primer extension. Nucleotide sequencing of the promoter region revealed the presence of a classical TATAA element and consensus sequences for binding the myeloid specific PU.1 factor and several lipopolysaccharide (LPS) (NF-IL6 and NF-kappa B) and interferon-gamma (IFN-gamma)-inducible response elements. Similar regulatory elements are found in the promoters of mouse and human NRAMP1. Northern blot analyses revealed NRAMP1 expression in reticuloendothelial organs (spleen and liver), lung, and thymus. As demonstrated in mice and humans, the macrophage is also a major site of NRAMP1 mRNA expression in chickens. However, the high levels of expression detected in chicken thymus contrast with the absence of expression of the mammalian Nramp1 gene in this tissue.