Aminomethyltransferase (Amt), also called glycine cleavage system T-protein is an important enzyme in glycine metabolism (EC 2.1.2.10). Mutations in this gene in humans lead to nonketotic hyperglycinemia, a fatal Mendelian disease. Here, we report the cloning and sequencing of the murine Amt gene. The murine Amt gene consists of nine closely spaced exons that are contained within approximately 5 kb of genomic DNA. It encodes a protein of 403 amino acids that is highly homologous to other mammalian aminomethyltransferases. The cis-acting promoter of the Amt gene is likely to be very short as immediately upstream of the murine Amt gene another gene termed Nicolin 1 gene (Nicn1) is located.