Evolution of the A+T-rich region of mitochondrial DNA in the melanogaster species subgroup of Drosophila |
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Authors: | Tsujino Fumi Kosemura Akiko Inohira Kayo Hara Toshiko Otsuka Yoko F Obara Mari K Matsuura Etsuko T |
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Institution: | (1) Department of Biology, Ochanomizu University, Otsuka 2-1-1, Bunkyo-ku, Tokyo 112-8610, Japan, JP |
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Abstract: | We determined the nucleotide sequences of two regions in the A+T-rich region of mitochondrial DNA (mtDNA) in the siI and siII
types of D. simulans, the maII type of D. mauritiana, and D. sechellia. The sequences were aligned with those of the corresponding
regions of siIII of D. simulans and maI of D. mauritiana, D. melanogaster, and D. yakuba. The type I and type II elements
and the T-stretches were detected in all eight of the mtDNA types compared, indicating that the three elements are essential
in the A+T-rich region of this species subgroup. The alignment revealed several short repetitive sequences and relatively
large deletions in the central portions of the region. In the highly conserved sequence elements in the type II elements,
the substitution rates were not uniform among lineages and acceleration in the substitution rate might have been due to loss
of functional constraint in the stem–loop-forming sequences predicted in the type II elements. Patterns of nucleotide substitutions
observed in the A+T-rich region were further compared with those in the coding regions and in the intergenic regions of mtDNA.
Substitutions between A and T were particularly repressed in the highly conserved sequence elements and in the intergenic
regions compared with those in the A+T-rich region excluding the highly conserved sequence elements and in the fourfold degenerate
sites in the coding regions. The functional and structural characteristics of the A+T-rich region that might be involved in
this substitutional bias are discussed. |
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