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MBE Advance Access published online on January 24, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msm245
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© The Author 2008. 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 Article

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

David R. Smith1 and Robert W. Lee1

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

Corresponding Author: Robert W. Lee, Department of Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada. Phone: 902.494.2554 FAX: 902.494.3736 e-mail: robert.lee{at}dal.ca

Received for publication July 9, 2007. Revision received October 26, 2007. Revision received 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 kilobase (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


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