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Nucleic Acids Research 2005 33(12):3812-3820; doi:10.1093/nar/gki693
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Published online 8 July 2005

© The Author 2005. Published by Oxford University Press. All rights reserved
The online version of this article has been published under an open access model. Users are entitled to use, reproduce, disseminate, or display the open access version of this article for non-commercial purposes provided that: the original authorship is properly and fully attributed; the Journal and Oxford University Press are attributed as the original place of publication with the correct citation details given; if an article is subsequently reproduced or disseminated not in its entirety but only in part or as a derivative work this must be clearly indicated. For commercial re-use, please contact journals.permissions{at}oupjournals.org

Article

Contrahelicase activity of the mitochondrial transcription termination factor mtDBP

Paola Loguercio Polosa1, Stefania Deceglie1, Marina Roberti1, Maria Nicola Gadaleta1,2 and Palmiro Cantatore1,2,*

1Dipartimento di Biochimica e Biologia Molecolare, Università degli Studi di Bari Via Orabona, 4, 70125 Bari, Italy 2Istituto di Biomembrane e Bioenergetica, CNR Via Amendola, 165/A, 70126 Bari, Italy

*To whom correspondence should be addressed at Dipartimento di Biochimica e Biologia Molecolare, Università degli Studi di Bari, Via Orabona, 4, 70125 Bari, Italy. Tel: +39 080 5443378; Fax: +39 080 5443403; Email: p.cantatore{at}biologia.uniba.it

Received March 15, 2005. Revised June 3, 2005. Accepted June 16, 2005.

The sea urchin mitochondrial D-loop binding protein (mtDBP) is a transcription termination factor that is able to arrest bidirectionally mitochondrial RNA chain elongation. The observation that the mtDBP binding site in the main non-coding region is located in correspondence of the 3' end of the triplex structure, where the synthesis of heavy strand mitochondrial (mt) DNA is either prematurely terminated or allowed to continue, raised the question whether mtDBP could also regulate mtDNA replication. By using a helicase assay in the presence of the replicative helicase of SV40, we show that mtDBP is able to inhibit the enzyme thus acting as a contrahelicase. The impairing activity of mtDBP is bidirectional as it is independent of the orientation of the protein binding site. The inhibition is increased by the presence of the guanosine-rich sequence that flanks mtDBP binding site. Finally, a mechanism of abrogation of mtDBP contrahelicase activity is suggested that is based on the dissociation of mtDBP from DNA caused by the passage of the RNA polymerase through the protein–DNA complex. All these findings favour the view that mtDBP, besides serving as transcription termination factor, could also act as a negative regulator of mtDNA synthesis at the level of D-loop expansion.


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