Extrachromosomal DNA in the Apicomplexa
Extrachromosomal DNA adds a new dimension to genetic studies in the Apicomplexa. At a fundamental level, it has the potential to give a new perspective on evolutionary relationships between various taxa. Unlike the polymorphic diversity of many malarial chromosomal genes, a high level of sequence conservation is apparent in the malarial extrachromosomal DNAs that have been examined [Feagin, 1992] suggesting that they will be useful in tracing the evolution of taxa and genetically defined populations. In addition, and in more practical terms, analysis of extrachromosomal DNA may help with the application of specific chemotherapeutic intervention to organellar metabolic pathways. Although it might be argued that these aspects are rather limited, the finding that in malaria there are two unrelated forms of extrachromosomal DNA with organellar characteristics [Wilson et al., 1991; Feagin et al., 1992] is both unexpected and of general scientific interest. Consequently, a full description of the extrachromosomal DNAs in Apicomplexans should be made to complement other studies, such as the construction of chromosomal maps, that aim to improve our understanding of the genetics of important pathogenic organisms like Toxoplasma and Plasmodium.
KeywordsInverted Repeat Toxoplasma Gondii Plasmodium Knowlesi Cruciform Structure Gene Cytochrome Oxidase
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