Isolation and mapping of the first ruminant multidrug resistance genes

The first ruminant multiple drug resistance gene (MDR1) has been cloned and sequenced from sheep. Sequence data revealed the sheep MDR1 gene to have h igh sequence and structural similarity to other characterized MDR proteins from humans and rodents. A restriction fragment length polymorphism was dis covered using the EcoRI enzyme and used to map the MDR1 gene to sheep chrom osome 4. Physical mapping using fluorescent in situ hybridisation confirmed this map placement and assigned the MDR1 locus in the region 4q15-q21. The ovine MDR2 gene was also cloned and found to map to the same region as MDR 1.