AbstractBackground: Fanconi anaemia (FA) is an autosomal recessive chromosomal instability disorder. Six distinct FA disease genes have been identified, the products of which function in an integrated pathway that is thought to support a nuclear caretaker function. Comparison of FA gene characteristics in different species may help to unravel the molecular function of the FA pathway.Results: We have cloned the murine homologue of the Fanconi anaemia complementation group G gene, FANCG/XRCC9. The murine Fancg protein shows an 83% similarity to the human protein sequence, and has a predicted molecular weight of 68.5 kDa. Expression of mouse Fancg in human FA‐G lymphoblasts fully corrects their cross‐linker hypersensitivity. At mRNA and protein levels we detected the co‐expression of Fancg and Fanca in murine tissues. In addition, mouse Fancg and Fanca proteins co‐purify by immunoprecipitation. Upon transfection into Fanca‐deficient mouse embryonic fibroblasts EGFP‐Fancg chimeric protein was detectable in the nucleus.Conclusions: We identified a murine cDNA, Fancg, which cross‐complements the cellular defect of human FA‐G cells and thus represents a true homologue of human FANCG. Spleen, thymus and testis showed the highest Fancg expression levels. Although Fancg and Fanca are able to form a complex, this interaction is not required for Fancg to accumulate in the nuclear compartment.