Mammalian BEX, WEX and GASP genes: coding and non-coding chimaerism sustained by gene conversion events.
BACKGROUND
The identification of sequence innovations in the genomes of mammals facilitates understanding of human gene function, as well as sheds light on the molecular mechanisms which underlie these changes. Although gene duplication plays a major role in genome evolution, studies regarding concerted evolution events among gene family members have been limited in scope and restricted to protein-coding regions, where high sequence similarity is easily detectable.


RESULTS
We describe a mammalian-specific expansion of more than 20 rapidly-evolving genes on human chromosome Xq22.1. Many of these are highly divergent in their protein-coding regions yet contain a conserved sequence motif in their 5' UTRs which appears to have been maintained by multiple events of concerted evolution. These events have led to the generation of chimaeric genes, each with a 5' UTR and a protein-coding region that possess independent evolutionary histories. We suggest that concerted evolution has occurred via gene conversion independently in different mammalian lineages, and these events have resulted in elevated G+C levels in the encompassing genomic regions. These concerted evolution events occurred within and between genes from three separate protein families ('brain-expressed X-linked' [BEX], WWbp5-like X-linked [WEX] and G-protein-coupled receptor-associated sorting protein [GASP]), which often are expressed in mammalian brains and associated with receptor mediated signalling and apoptosis.


CONCLUSIONS
Despite high protein-coding divergence among mammalian-specific genes, we identified a DNA motif common to these genes' 5' UTR exons. The motif has undergone concerted evolution events independently of its neighbouring protein-coding regions, leading to formation of evolutionary chimaeric genes. These findings have implications for the identification of non protein-coding regulatory elements and their lineage-specific evolution in mammals.
Winter
Eitan E
EE
Department of Human Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, UK. eew@sanger.ac.uk
Ponting
Chris P
CP
D020121:5' Untranslated Regions; D020816:Amino Acid Motifs; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D002645:Chickens; D046528:Chimerism; D002874:Chromosome Mapping; D041321:Chromosomes, Human, X; D030541:Databases, Genetic; D004285:Dogs; D019143:Evolution, Molecular; D005091:Exons; D005785:Gene Conversion; D016678:Genome; D015894:Genome, Human; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis; D002679:Pan troglodytes; D010802:Phylogeny; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D013045:Species Specificity; D033921:Vesicular Transport Proteins / Q000235:genetics*
D020121:5' Untranslated Regions; C469586:BEX1 protein, human; D002352:Carrier Proteins; C463459:GPRASP1 protein, human; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D033921:Vesicular Transport Proteins