GENE STRUCTURE OF HUMAN AND MOUSE METHYLENETETRAHYDROFOLATE REDUCTASE(MTHFR)

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the conversion o f 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a co-sub strate for homocysteine remethylation to methionine. A human cDNA for MTHFR, 2.2 kb in length, has been expressed and shown to result in a c atalytically active enzyme of approximately 70 kDa. Fifteen mutations have been identified in the MTHFR gene: 14 rare mutations associated w ith severe enzymatic deficiency and 1 common variant associated with a milder deficiency. The common polymorphism has been implicated in thr ee multifactorial diseases: occlusive vascular disease, neural tube de fects, and colon cancer. The human gene has been mapped to chromosomal region 1p36.3 while the mouse gene has been localized to distal Chrom osome (Chr) 4. Here we report the isolation and characterization of th e human and mouse genes for MTHFR. A human genomic clone (17 kb) was f ound to contain the entire cDNA sequence of 2.2 kb; there were 11 exon s ranging in size from 102 bp to 432 bp. Intron sizes ranged from 250 bp to 1.5 kb with one exception of 4.2 kb. The mouse genomic clones (1 9 kb) start 7 kb 5' exon 1 and extend to the end of the coding sequenc e. The mouse amino acid sequence is approximately 90% identical to the corresponding human sequence. The exon sizes, locations of intronic b oundaries, and intron sizes are also quite similar between the two spe cies. The availability of human genomic clones has been useful in de s igning primers for exon amplification and mutation detection. The mous e genomic clones will be helpful in designing constructs for gene targ eting and generation of mouse models for MTHFR deficiency.