title: Contrahelicase activity of the mitochondrial transcription termination factor mtDBP.
abstract: 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.
authors: Dipartimento di Biochimica e Biologia Molecolare, Università degli Studi di Bari Via Orabona, 4, 70125 Bari, Italy.
authors: Paola Loguercio
authors: PL
authors: Polosa
authors: Stefania
authors: S
authors: Deceglie
authors: Marina
authors: M
authors: Roberti
authors: Maria Nicola
authors: MN
authors: Gadaleta
authors: Palmiro
authors: P
authors: Cantatore
mesh_terms: D000818:Animals; D004265:DNA Helicases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D013539:Simian virus 40 / Q000201:enzymology; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D014157:Transcription Factors; C119291:mitochondrial D-loop-binding protein, Paracentrotus lividus; D004265:DNA Helicases