We have cloned a novel mouse cDNA, Aup1, encoding a predicted protein of 410 amino acid residues. The 1.5-kb Aup1 transcript is ubiquitously expressed in mouse tissues. An evolutionary relationship to the Caenorhabditis elegans predicted protein F44b9.5 is indicated by the 35% identity and 53% conservation of the amino acid sequences. Nineteen related human ESTs spanning 80% of the protein have also been identified, with a predicted amino acid sequence identity of 86% between the human and the mouse proteins. The gene has been mapped to a conserved linkage group on human chromosome 2p13 and mouse Chromosome 6. Aup1 was eliminated as a candidate gene for two closely linked disorders, human LGMD2B and mouse mnd2.