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MBE Advance Access originally published online on January 24, 2008
Molecular Biology and Evolution 2008 25(3):487-496; doi:10.1093/molbev/msm245
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© The Author 2007. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Articles

Mitochondrial Genome of the Colorless Green Alga Polytomella capuana: A Linear Molecule with an Unprecedented GC Content

David R. Smith and Robert W. Lee

Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada

E-mail: robert.lee{at}dal.ca.

Accepted for publication November 1, 2007.

One common observation concerning mitochondrial genomes is that they have a low guanine and cytosine content (GC content); of the complete mitochondrial genome sequences currently available at the National Center for Biotechnology Information (NCBI) (July 2007), the GC content ranges from 13.3% to 53.2% and has an average value of 38%. Here, we present the GC-rich mitochondrial genome (57% GC) of the colorless green alga Polytomella capuana. The disproportion of GC among the different regions of the P. capuana mitochondrial DNA (mtDNA) suggests that a neutral process is responsible for the GC bias. We propose that a biased gene conversion mechanism resulted in the GC-rich state of the P. capuana mtDNA. In addition, our analysis indicates that the P. capuana mitochondrial genome is a single 13-kb linear molecule with telomeres, which have a closed (hairpin-loop) conformation: a novel terminal structure among described linear green-algal mtDNAs. Furthermore, using a series of GC-rich inverted repeats found within the P. capuana mitochondrial genome, we describe recombination-based scenarios of how intact linear mtDNA conformations can be converted into the fragmented forms found in other Polytomella taxa.

Key Words: Polytomella capuana • green algae • mitochondrial DNA (mtDNA) • GC content • biased gene conversion • telomeres

Charles Delwiche, Associate Editor


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