The mouse salivary androgen-binding protein (ABP) gene cluster on chromosomes 7: characterization and evolutionary relationships.

Mouse salivary androgen-binding protein (ABP) is a pair of dimers, composed of an alpha subunit disulfide bridged to either a beta or a gamma subunit. It has been proposed that each subunit is encoded by a distinct gene: Abpa, Abpb, and Abpg for the alpha, beta, and gamma subunits, respectively. We report here the structures and sequences of the genes that encode these three subunits. Each gene has three exons separated by two introns. Mouse salivary ABP is a member of the secretoglobin family, and we compare the structure of the three ABP subunit genes to those of 18 other mammalian secretoglobins. We map the three genes as a gene cluster located 10 cM from the centromere of Chromosome (Chr) 7 and show that Abpa is the closest of the three to the gene for glucose phosphate isomerase (GPI) and that Abpg is the closest to the centromere, with Abpb mapping between them. Abpa is oriented in the opposite direction to Abpb and Abpg, with its 5' end directed toward their 5' ends. We compare the location of these genes with other secretoglobin genes in the mouse genome and with the known locations of secretoglobin genes in the human genome and present evidence that strong positive selection has driven the divergence of the coding regions of Abpb and Abpg since the putative duplication event that created them.