CHARACTERIZATION OF A CLUSTER OF SULFATASE GENES ON XP22.3 SUGGESTS GENE DUPLICATIONS IN AN ANCESTRAL PSEUDOAUTOSOMAL REGION

An obligatory crossing-over event between the X and Y chromosomes in m ammals occurs at each male meiosis within the 2.6 Mb of DNA defining t he pseudoautosomal region (PAR). Genes located within or near the huma n PAR have homologous copies on the X and Y chromosomes, escape X inac tivation and appear to be highly divergent throughout evolution, We ha ve characterized the genomic structure of two genes from a recently id entified cluster of sulfatase genes (ARSD and ARSE) located in the Xp2 2.3 region, and of their homologs on the Y chromosome. Our results ind icate that the ARSD and ARSE genes from within this cluster have a con served genomic organization, shared also by another Xp22.3 gene, STS, but completely different from that of all the other sulfatase genes, S equence analysis of the Y-linked homologs indicate that they represent truncated pseudogenes, Sequence identity values between the X and Y c opies of each gene is on average 91%, significantly higher than the va lues obtained by comparing different members of the family, FISH mappi ng experiments performed in several primate species revealed an identi cal localization of the X-linked copies to that in man, but different localizations of the Y homologs, Together, our data indicate that the cluster of sulfatase genes on human Xp22.3 was created through duplica tion events which probably occurred in an ancestral PAR, and support t he view that the PAR has undergone multiple changes during recent mamm alian evolution.