Hudspeth, Michael E. S.
M.S. (Master of Science)
Department of Biological Sciences
Cytochrome oxidase; Cytogenetics; DNA
Previous characterization of P. megasperma mitochondrial DNAs revealed two genic inversions between a host-specific and a nonspecific strain. As part of a characterization of oomycete mitochondrial genomes, studies of the nucleotide sequence of the region involving the COI-COII inversion were initiated. The COII genic region was localized, cloned and sequenced. The COII gene encodes a 258 amino acid protein with an approximate molecular weight of 29.6Kd. The data strongly suggests a lack of introns in this gene. The COI protein has been found to be encoded 235bp downstream from COII on the same strand. The translated COII amino acid sequence exhibits a greater than 50$ amino acid homology with other characterized eukaryotic COII proteins, being most homologous with those of plants. The two functionally conserved membrane-spanning helices and the putative copper-binding site, along with other conserved regions, have been identified in the protein. The genic region has an A-T content of 71$. Flanking regions contain 79$ and 90$ A-T contents. As expected for A-T-rich genomes, codon usage tables indicate a strong bias for the use of a third position A/T when choices exist. Of all codons within this gene, 85$ terminate in an A or T. Remarkably, however, all 7 Trp codons are TGG instead of the preferred TGA typical of all but plant mitochondria using a modified genetic code. This would lead to the conclusion that in Phytophthora mitochondrial DNA, TGA is either a stop codon, as it is in plant mitochondria, or an infrequently used trp codon.
Sachay, Donna Jean, "The absence of TGA codons in the DNA sequence of the Phytophthora megasperma gene for cytochrome c oxidase subunit II" (1989). Graduate Research Theses & Dissertations. 5278.
[vii], 69 pages
Northern Illinois University
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