Genomic structure and chromosome mapping of the genes encoding clathrin-associated adaptor medium chains μ1A (Ap1m1) and μ1B (Ap1m2)

The protein μ1B is a member of the medium chain family of the clathrin-associated adaptor complex and is expressed exclusively in epithelial cells. We determined the genomic structure of previously cloned murine genes for μ1B (Ap1m2) and its closely related homolog, μ1A (Ap1m1). Comparison of their genomic structures revealed that the positions of introns are identical between these two genes, except for the insertion of an additional intron in Ap1m1 (intron 4). By contrast, these structures are different from that of the more distantly related Ap2m1 gene encoding μ2. Taken together with the similarity of amino acid sequences among these genes, the data presented in this study suggest that Ap1m1/2 and Ap2m1 diverged long before the separation of Ap1m1 and Ap1m2, which most likely resulted from a relatively recent gene duplication. We also mapped AP1M2 to human chromosome 19p13.2 and Ap1m2 to the proximal region of mouse chromosome 9. The results are consistent with the fact that these regions are syntenic.