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The in vivo conformation of the plastid DNA of toxoplasma gondii : implications for replication.

Williamson, D. H. and Denny, P. W. and Moore, P. W. and Sato, S. and McCready, S. and Wilson, R. J. M. (2001) 'The in vivo conformation of the plastid DNA of toxoplasma gondii : implications for replication.', Journal of molecular biology., 306 (2). pp. 159-168.


The Phylum Apicomplexa comprises thousands of obligate intracellular parasites, some of which cause serious disease in man and other animals. Though not photosynthetic, some of them, including the malaria parasites (Plasmodium spp.) and the causative organism of Toxoplasmosis, Toxoplasma gondii, possess a remnant plastid partially determined by a highly derived residual genome encoded in 35 kb DNA. The genetic maps of the plastid genomes of these two organisms are extremely similar in nucleotide sequence, gene function and gene order. However, a study using pulsed field gel electrophoresis and electron microscopy has shown that in contrast to the malarial version, only a minority of the plastid DNA of Toxoplasma occurs as circular 35 kb molecules. The majority consists of a precise oligomeric series of linear tandem arrays of the genome, each oligomer terminating at the same site in the genetic map, i.e. in the centre of a large inverted repeat (IR) which encodes duplicated tRNA and rRNA genes. This overall topology strongly suggests that replication occurs by a rolling circle mechanism initiating at the centre of the IR, which is also the site at which the linear tails of the rolling circles are processed to yield the oligomers. A model is proposed which accounts for the quantitative structure of the molecular population. It is relevant that a somewhat similar structure has been reported for at least three land plant chloroplast genomes.

Item Type:Article
Keywords:Apicomplexan plastid, Toxoplasma gondii, 35 kb genome,; DNA topology, Rolling circle replication, Field gel-electrophoresis, Rolling-circle replication, Electron-microscopic localization, Parasite plasmodium-falciparum;chenopodium-album l, Mitochondrial-DNA, C.
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Record Created:11 May 2009 11:50
Last Modified:09 Jun 2009 15:51

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