Journal Article

Pseudogenes, Junk DNA, and the Dynamics of Rickettsia Genomes

Jan O. Andersson and Siv G. E. Andersson

in Molecular Biology and Evolution

Published on behalf of Society for Molecular Biology and Evolution

Volume 18, issue 5, pages 829-839
Published in print May 2001 | ISSN: 0737-4038
Published online May 2001 | e-ISSN: 1537-1719 | DOI: http://dx.doi.org/10.1093/oxfordjournals.molbev.a003864
Pseudogenes, Junk DNA, and the Dynamics of Rickettsia Genomes

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Studies of neutrally evolving sequences suggest that differences in eukaryotic genome sizes result from different rates of DNA loss. However, very few pseudogenes have been identified in microbial species, and the processes whereby genes and genomes deteriorate in bacteria remain largely unresolved. The typhus-causing agent, Rickettsia prowazekii, is exceptional in that as much as 24% of its 1.1-Mb genome consists of noncoding DNA and pseudogenes. To test the hypothesis that the noncoding DNA in the R. prowazekii genome represents degraded remnants of ancestral genes, we systematically examined all of the identified pseudogenes and their flanking sequences in three additional Rickettsia species. Consistent with the hypothesis, we observe sequence similarities between genes and pseudogenes in one species and intergenic DNA in another species. We show that the frequencies and average sizes of deletions are larger than insertions in neutrally evolving pseudogene sequences. Our results suggest that inactivated genetic material in the Rickettsia genomes deteriorates spontaneously due to a mutation bias for deletions and that the noncoding sequences represent DNA in the final stages of this degenerative process.

Journal Article.  7213 words.  Illustrated.

Subjects: Evolutionary Biology ; Molecular and Cell Biology

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