Mouse alpha-1-microglobulin/bikunin precursor: cDNA analysis, gene evolution and physical assignment of the gene next to the orosomucoid locus.

alpha-1-Microglobulin (A1m) is a member of the lipocalin superfamily whereas bikunin is a Kunitz-type proteinase inhibitor. A1m and bikunin originate from a shared precursor. A comparison of mammalian cDNAs for the precursor indicates a highly conserved amino acid sequence along with muridae-specific deletions in both A1m and bikunin. In rodents, the gene for this precursor is less than 300 kb apart from the orosomucoid gene, another lipocalin gene. This precursor likely results from the assembly of two lipocalin and Kunitz-type genes, between 270 and 80 million years ago.