The functional intronless S-adenosylmethionine decarboxylase gene of the mouse (Amd-2) is linked to he ornithine decarboxylase gene (Odc) on Chromosome 12 and is present in distantly related species of the genus Mus

S-Adenosylmethionine decarboxylase (AdoMetDC) is a key enzyme in the biosyn thesis of polyamines. We have previously identified a mouse AdoMetDC gene t hat exhibits the hallmarks of a retroposon; that is, it has no introns, is flanked by direct repeats, and has a poly(dA) tract at its 3'-end. This gen e, termed Amd-2, is not a processed pseudogene; rather, it is transcribed i n a variety of mouse tissues and encodes a functional enzyme. In the curren t report, we present the sequence of a 6.7-kb genomic segment of the Amd-2 locus. Several sequences of interest, including an intercisternal A particl e (IAP) element, a transposon-related sequence, and several expressed seque nce tags (ESTs), were found within or near Amd-2 We also show, through anal ysis of an interspecific backcross, that Amd-2 is located on Chr 12 tightly linked to the gene (Odc) that encodes ornithine decarboxylase, another key enzyme in polyamine synthesis. Finally, we show that Amd-2 is present amon g several divergent species of the genus Mus. Thus, the integration event t hat generated Amd-2 may have occurred early during Mus evolution.