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UAG is a sense codon in several chlorophycean mitochondria
Y Hayashi-Ishimaru1, T Ohama, Y Kawatsu
1Biohistory Research Hall, 1-1 Murasaki-cho, Takatsuki, Osaka 569, Japan.
Current Genetics
|June 1, 1996
Summary
Green algae exhibit a deviant mitochondrial genetic code, a first for this group. Specific species use non-universal codons (UAG) for alanine or leucine, suggesting evolutionary changes in release factors.
Area of Science:
- Mitochondrial genetics
- Algal evolutionary biology
Background:
- The mitochondrial genetic code is typically universal across land plants and green algae.
- A red alga, Chondrus crispus, is the only previously known alga with a deviant mitochondrial code (UGA=Trp).
Purpose of the Study:
- To investigate potential deviations in the mitochondrial genetic code of green algae.
- To identify species with non-universal codon usage in their mitochondrial DNA.
Main Methods:
- Analysis of 366-bp DNA sequences of the mitochondrial cytochrome oxidase subunit I (COXI) gene.
- Comparative sequence analysis with other algae and land plants.
- Phylogenetic analysis of COXI sequences.
Main Results:
- Five of ten chlorophyceaen algae species examined showed 3-8 in-frame UAG codons.
- In Hydrodictyon reticulatum, Pediastrum boryanum, and Tetraedron bitridens, UAG codons likely code for alanine.
- In Coelastrum microporum and Scenedesmus quadricauda, UAG codons likely code for leucine.
- Species with UAG coding for alanine share zoospore formation, while those coding for leucine form daughter coenobia.
- No genetic code deviation was found in the remaining five species.
Conclusions:
- This study reports the first instance of a deviant mitochondrial genetic code in green algae.
- Mutations in release factors affecting UAG codons are implicated in these code changes.
- The findings suggest distinct evolutionary pathways within green algae based on mitochondrial genetic code variations.