| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 1999: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1998: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Research Abstract |
We determined the nucleotide sequences of the two regions (A and B) within the A+T-rich region of mitochondrial DNA (mtDNA) in D. simulans (siI), D. mauritiana (maII), and D. sechellia. The sequences of these three mtDNA types were aligned with the corresponding sequences of D. melanogaster, D. simulans (siII, siIII), D. mauritiana (maI), and D. yakuba. The sequences included regions that correspond to the type I and type II elements, the highly conserved sequence elements within the type II elements, and the T-stretches in D. melanogaster. Each mtDNA type was characterized by unique sequences in the B region of D. simulans, D. mauritiana and D. sechellia, and short tandem repeats in D. melanogaster, D.simulans (siI) and D. mauritiana (maII).
In the highly conserved sequence elements in both A and B regions, the accelerated rates of nucleotide substitution were confirmed in D. melanogaster. In D. sechellia, D. simulans (siI), and the 1st element in D. simulans (siII) which contained two
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large deletions within the element, the relatively high rates of nucleotide substitution were also observed. The acceleration might be due to the loss of functional constraint in the sequences involved in stem-loop forming. In the other regions within the A and B regions, the rates of nucleotide substitution were as expected from the phylogenetic relationship among the eight mtDNA types using the coding sequences in the mitochondrial genome.
To identify the sequences forming stem-loop structures, the sequences were examined by the program mfold as well as by S1 nuclease. The recognition sites of S1 nuclease were roughly coincided with the predictions by mfold for the highly conserved sequence elements. In a clone containing a complete type II repeat in the maII type, only one site was recognized by S1 nuclease, despite that mfold predicted two such sequences.
These results suggested that functional sequences within the highly conserved sequence elements have been maintained in the type II repeat, and that a stable stem-loop structure is determined, by some regulating mechanism, at the central portion of the A+T-rich region. Less
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