A gene recently inactivated in human defines a new olfactory receptor family in mammals

The olfactory receptor (OR) gene family constitutes one of the largestmultigene families and is distributed among many chromosomal sites in thehuman genome. Four OR families have been defined in mammals. We previouslydemonstrated that a high fraction of human OR sequences have incurreddeleterious mutations, thus reducing the repertoire of functional OR genes.In this study, we have characterized a new OR gene, 912-93, in primates.This gene is unique and it defines a new OR family. It localizes to humanchromosome 11q11-12 and at syntenical sites in other hominoids. Thesequence marks a previously unrecognized rearrangement of pericentromericmaterial from chromosome 11 to the centromeric region of gibbon chromosome5. The human gene contains a nonsense point mutation in the regioncorresponding to the extracellular N-terminus of the receptor. Thismutation is present in humans of various ethnic groups, but is absent inapes, suggesting that it probably appeared during the divergence of humansfrom other apes, <4 000 000-5 000 000 years ago. A second mutation, aframeshift at a different location, has occurred in the gorilla copy ofthis gene. These observations suggest that OR 912-93 has been recentlysilenced in human and gorilla, adding to a pool of OR pseudogenes whosegrowth may parallel a reduction in the sense of smell in primates.