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Nucleic Acids Research Advance Access originally published online on July 22, 2009
Nucleic Acids Research 2009 37(17):5701-5713; doi:10.1093/nar/gkp614
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Nucleic Acids Research, 2009, Vol. 37, No. 17 5701-5713
© 2009 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Genome Integrity, Repair and Replication

The accessory subunit of mitochondrial DNA polymerase {gamma} determines the DNA content of mitochondrial nucleoids in human cultured cells

M. Di Re1, H. Sembongi1, J. He1, A. Reyes1, T. Yasukawa1, P. Martinsson2, L. J. Bailey1, S. Goffart2, J. D. Boyd-Kirkup1, T. S. Wong3, A. R. Fersht3, J. N. Spelbrink2 and I. J. Holt1,*

1MRC-Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK, 2Institute of Medical Technology and Tampere University Hospital, FI-33014 University of Tampere, Finland and 3MRC Centre for Protein Engineering, Medical Research Council, Hills Road, Cambridgae, CB2 0QH, UK

*To whom correspondence should be addressed. Tel: + 44 12 23 25 28 40; Fax: + 44 12 23 25 28 45; Email: holt{at}mrc-mbu.cam.ac.uk

Received June 10, 2009. Revised July 6, 2009. Accepted July 7, 2009.

The accessory subunit of mitochondrial DNA polymerase {gamma}, POLGβ, functions as a processivity factor in vitro. Here we show POLGβ has additional roles in mitochondrial DNA metabolism. Mitochondrial DNA is arranged in nucleoprotein complexes, or nucleoids, which often contain multiple copies of the mitochondrial genome. Gene-silencing of POLGβ increased nucleoid numbers, whereas over-expression of POLGβ reduced the number and increased the size of mitochondrial nucleoids. Both increased and decreased expression of POLGβ altered nucleoid structure and precipitated a marked decrease in 7S DNA molecules, which form short displacement-loops on mitochondrial DNA. Recombinant POLGβ preferentially bound to plasmids with a short displacement-loop, in contrast to POLG{alpha}. These findings support the view that the mitochondrial D-loop acts as a protein recruitment centre, and suggest POLGβ is a key factor in the organization of mitochondrial DNA in multigenomic nucleoprotein complexes.

The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.


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