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J Biol Chem. 2010 Mar 5;285(10):7056-66. doi: 10.1074/jbc.M109.084038. Epub 2009 Dec 30.

TbPIF1, a Trypanosoma brucei mitochondrial DNA helicase, is essential for kinetoplast minicircle replication.

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Department of Biological Chemistry, Johns Hopkins Medical School, Baltimore, Maryland 21205, USA.


Kinetoplast DNA, the trypanosome mitochondrial genome, is a network of interlocked DNA rings including several thousand minicircles and a few dozen maxicircles. Minicircles replicate after release from the network, and their progeny reattach. Remarkably, trypanosomes have six mitochondrial DNA helicases related to yeast PIF1 helicase. Here we report that one of the six, TbPIF1, functions in minicircle replication. RNA interference (RNAi) of TbPIF1 causes a growth defect and kinetoplast DNA loss. Minicircle replication intermediates decrease during RNAi, and there is an accumulation of multiply interlocked, covalently closed minicircle dimers (fraction U). In studying the significance of fraction U, we found that this species also accumulates during RNAi of mitochondrial topoisomerase II. These data indicate that one function of TbPIF1 is an involvement, together with topoisomerase II, in the segregation of minicircle progeny.

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