We analyzed the origin of allelic diversity at the class II HLA-DRB1 locus, using a complex microsatellite located in intron 2, close to the polymorphic second exon. A phylogenetic analysis of human, gorilla, and chimpanzee DRB1 sequences indicated that the structure of the microsatellite has evolved, primarily by point mutations, from a putative ancestral (GT)x(GA)y-complex-dinucleotide repeat. In all contemporary DRB1 allelic lineages, with the exception of the human *04 and the gorilla *08 lineages, the (GA)y repeat is interrupted, often by a G-->C substitution. In general, the length of the 3' (GA)y repeat correlates with the allelic lineage and thus evolves more slowly than a middle (GA)z repeat, whose length correlates with specific alleles within the lineage. Comparison of the microsatellite sequence from 30 human DRB1 alleles showed the longer 5' (GT)x to be more variable than the shorter middle (GA)z and 3' (GA)y repeats. Analysis of multiple samples with the same exon sequence, derived from different continents, showed that the 5' (GT)x repeat evolves more rapidly than the middle (GA)z and the 3' (GA)y repeats, which is consistent with findings of a higher mutation rate for longer tracts. The microsatellite-repeat-length variation was used to trace the origin of new DRB1 alleles, such as the new *08 alleles found in the Cayapa people of Ecuador and the Ticuna people of Brazil.
Pubmed ID: 10330359 RIS Download
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Software integrated tool for conducting automatic and manual sequence alignment, inferring phylogenetic trees, mining web based databases, estimating rates of molecular evolution, and testing evolutionary hypotheses. Used for comparative analysis of DNA and protein sequences to infer molecular evolutionary patterns of genes, genomes, and species over time. MEGA version 4 expands on existing facilities for editing DNA sequence data from autosequencers, mining Web-databases, performing automatic and manual sequence alignment, analyzing sequence alignments to estimate evolutionary distances, inferring phylogenetic trees, and testing evolutionary hypotheses. MEGA version 6 enables inference of timetrees, as it implements RelTime method for estimating divergence times for all branching points in phylogeny.
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