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Identification and characterization of a second mouse Nramp gene
S Gruenheid1, M Cellier, S Vidal
1Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
Abstract:
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.
Insights
Researchers identified a new mouse gene, Nramp2, which is homologous to the Nramp gene involved in host resistance. Nramp2 is expressed in various tissues and mapped to mouse chromosome 15.
Area of Science:
- Genetics
- Molecular Biology
- Immunology
Background:
- The Nramp gene is a candidate for the Bcg/Ity/Lsh locus controlling natural resistance in mice.
- Host resistance genes play a crucial role in innate immunity against various infections.
Purpose of the Study:
- To isolate and characterize a second mouse Nramp gene, Nramp2.
- To analyze the Nramp2 gene's homology, expression, and chromosomal location.
Main Methods:
- Cross-hybridization using cDNA clones.
- Nucleotide and amino acid sequence analysis.
- Northern blotting for mRNA distribution.
- Genetic mapping using a polymorphic dinucleotide repeat.
Main Results:
- Nramp2 is a novel gene homologous to Nramp, forming a small gene family.
- Nramp2 encodes an integral membrane protein with significant structural similarity to Nramp.
- Nramp2 mRNA is expressed at low levels in all tested mouse tissues, unlike the macrophage-specific Nramp.
- Nramp2 was mapped to mouse chromosome 15.
Conclusions:
- Nramp2 represents a distinct but related gene to Nramp, potentially involved in host defense mechanisms.
- The widespread expression pattern of Nramp2 suggests roles beyond macrophage-specific immunity.
- The characterization of Nramp2 provides insights into the Nramp gene family and host resistance.