Nucleotide sequence and organization of the mouse adenine phosphoribosyltransferase gene: Presence of a coding region common to animal and bacterial phosphoribosyltransferases that has a variable intron/exon arrangement

We have determined the nucleotide sequence of a functional mouse adenine phosphoribosyltransferase (APRT) gene and its cDNA. The amino acid sequence of the enzyme is deduced from an open reading frame in the cDNA and predicts a protein with a molecular weight of 19,560. The protein coding region of the gene is ~2 kilobases, and it is composed of five exons and four introns. While the body of the gene is 53% G+C, the 200 nucleotides upstream from the ATG translation start codon are 66% G+C and contain three copies of the sequence C-C-G-C-C-C. The mouse APRT enzyme shares a homologous 20-amino acid sequence with mouse, hamster, and human hypoxanthine phosphoribosyltransferases (HPRTs) and several bacterial phosphoribosyltransferases. This sequence has previously been shown to be a likely catalytic domain in human HPRT and Escherichia coli glutamine phosphoribosyltransferase. Because of the similarities in function of these proteins, both eukaryotic and prokaryotic, it is not unexpected that they should exhibit one or more regions of homology, particularly at the 5-phosphoribosyl-1-pyrophosphate and purine binding sites, especially if they are related via a common evolutionary lineage. This homologous sequence is interrupted by a single intron in the mouse APRT gene and by two introns in the mouse HPRT gene. Furthermore, the positions of both introns in the HPRT sequence are different from that of the single intron in the corresponding sequence of the APRT gene.