Molecular cloning, expression and physical mapping of the human methionine synthase reductase gene

Methionine synthase reductase (EC 2.1.1.135) is a flavoprotein essential for maintenance of methionine synthase in an active state. We characterized the human gene for methionine synthase reductase (MTRR). The gene is approximately 34 kb and comprises 15 exons, varying in size from 43 to 1213 bp, and 14 introns whose sizes vary from 108 bp to 5 kb. The positions of several junctions are conserved between the MTRR gene and the C. elegans ortholog, as well as with the rat cytochrome P450 reductase gene. A 1.3 kb CpG island encompasses the 5'-flanking region and exon 1 and extends into intron 1. A short region including the transcription start site is sufficient to confer promoter activity, with a better outcome when accompanied by intron 1. The promoter region contains putative binding sites for Spl, AP-1, AP-2 as well as CAAT motifs, but no consensus TATA box. Primer extension analysis revealed a single major transcription start site, located 137 bp upstream of the previously reported initiator ATG. An alternative splicing event involving a portion of exon 1 predicts that translation can potentially be initiated at two different ATG codons. The gene was physically assigned to a narrow area between markers WI1755 and D5S1957. (C) 1999 Elsevier Science B.V. All rights reserved.