Gene Conversion Drives Within Genic Sequences: Concerted Evolution of Ribosomal RNA Genes in Bacteria and Archaea |
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Authors: | Daiqing Liao |
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Institution: | (1) Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, Sherbrooke, 3001 12e Avenue Nord, Québec, J1H 5N4 Canada, CA |
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Abstract: | Multiple copies of a given ribosomal RNA gene family undergo concerted evolution such that sequences of all gene copies are
virtually identical within a species although they diverge normally between species. In eukaryotes, gene conversion and unequal
crossing over are the proposed mechanisms for concerted evolution of tandemly repeated sequences, whereas dispersed genes
are homogenized by gene conversion. However, the homogenization mechanisms for multiple-copy, normally dispersed, prokaryotic
rRNA genes are not well understood. Here we compared the sequences of multiple paralogous rRNA genes within a genome in 12
prokaryotic organisms that have multiple copies of the rRNA genes. Within a genome, putative sequence conversion tracts were
found throughout the entire length of each individual rRNA genes and their immediate flanks. Individual conversion events
convert only a short sequence tract, and the conversion partners can be any paralogous genes within the genome. Interestingly,
the genic sequences undergo much slower divergence than their flanking sequences. Moreover, genomic context and operon organization
do not affect rRNA gene homogenization. Thus, gene conversion underlies concerted evolution of bacterial rRNA genes, which
normally occurs within genic sequences, and homogenization of flanking regions may result from co-conversion with the genic
sequence.
Received: 31 March 2000 / Accepted: 15 June 2000 |
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Keywords: | : Concerted evolution — Multigene families — rRNA — Gene conversion — Bacteria and Archaea — Comparative genomics |
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