title: Mitochondrial genome of the colorless green alga Polytomella capuana: a linear molecule with an unprecedented GC content.
abstract: 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.
authors.affiliation: Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: David R
authors.initials: DR
authors.lastname: Smith
authors.forename: Robert W
authors.initials: RW
authors.lastname: Lee
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D000460:Chlorophyta / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny
chemical_list: D004272:DNA, Mitochondrial