(1)Department of Membrane Research and Biophysics, The Weizmann Institute of Science, Rehovot, Israel
(2)The Genome Resource Core, The Weizmann Institute of Science, Rehovot, Israel
(3)Centre de Recherche en Biochimie Macromoléculaire, Montpellier, France
(4)Department of Chemistry and Biochemistry, University of Oklahoma, Oklahoma, USA
bmgustav@bioinfo.weizmann.ac.il
The human olfactory subgenome represents several hundred olfactory receptor (OR) genes in a dozen or more clusters on several chromosomes.
One OR gene cluster on human chromosome 17 (17p13.3) has been characterized in detail [1].
Four cosmids out of its minimal covering set (10 cosmids) were sequenced using a shotgun subcloning approach and automated sequencing.
Computer analysis [2] of the first sequenced cosmid (cos39) revealed three expected OR genes, as well as a new OR pseudogene (OR17-25), fused to a previously identified OR gene (OR17-24).
The mechanism for the generation of this doublet structure is analysed: we propose that it involved an initial duplication, and a subsequent deletion via non-homologous recombination.
The two other OR genes present in the cosmid (OR17-40 and OR17-228) may have evolved by way of tandem duplication of a 13.9 kb-long fragment, as first evidenced by the most significant signals in the autocorrelation algorithm employed.
MIR repeats are involved in the ancient (90 Myr) duplication event described.
Comparative analysis of the duplicated genes revealed a conserved gene structure: a long (5-6 kb) intron separates the intronless ~1 kb coding region from an upstream, short non-coding exon.
Furthermore, a conserved putative gene control region can be discerned.
All the OR genes found in cos39 belong to one subfamily.
Sequence analysis of three additional cosmids (cos73, cos46 and cos58) confirms that the proposed gene structure applies also to OR genes from a different family.
Four OR genes and an additional unexpected pseudogene were detected.
No additional, non-OR genes could be discerned within the OR gene cluster.
The sequenced cosmids include a plethora of interspersed repetitive sequences that integrated at different times, enabling us to reconstruct the evolutionary history of the gene cluster.
Several additional cosmids from this cluster are currently being sequenced, and the results provide additional information on the diversity, evolution and structure of the olfactory receptor genes.
REFERENCES
[1] Ben-Arie et al. (1993) Hum. Mol. Genet. 3:2, 229-235
[2] Glusman et al. (1996) Genomics, in press