The HMG-box mitochondrial transcription factor xl-mtTFA binds DNA as a tetramer to activate bidirectional transcription.
The mitochondrial HMG-box transcription factor xl-mtTFA activates bidirectional transcription by binding to a site separating two core promoters in Xenopus laevis mitochondrial DNA (mtDNA). Three independent approaches were used to study the higher order structure of xl-mtTFA binding to this site. First, co-immunoprecipitation of differentially tagged recombinant mtTFA derivatives established that the protein exists as a multimer. Second, in vitro chemical cross-linking experiments provided evidence of cross-linked dimers, trimers and tetramers of xl-mtTFA. Finally, high resolution scanning transmission electron microscopy (STEM) established that xl-mtTFA binds to the specific promoter-proximal site predominantly as a tetramer. Computer analysis of several previously characterized binding sites for xl-mtTFA revealed a fine structure consisting of two half-sites in a symmetrical orientation. The predominant sequence of this dyad symmetry motif shows homology to binding sites of sequence-specific HMG-box-containing proteins such as Sry and Lef-1. We suggest that bidirectional activation of transcription results from the fact that binding of a tetramer of xl-mtTFA permits symmetrical interactions with other components of the transcription machinery at the adjacent core promoters.
Antoshechkin
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Department of Pharmacological Sciences, State University of New York at Stony Brook, 11794-8651, USA.
Bogenhagen
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DF
Mastrangelo
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IA
D000818:Animals; D001665:Binding Sites; D016384:Consensus Sequence; D003432:Cross-Linking Reagents; D004272:DNA, Mitochondrial / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D005976:Glutaral / Q000494:pharmacology; D006609:High Mobility Group Proteins / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D008928:Mitochondria / Q000235:genetics*; D009698:Nucleoproteins / Q000648:ultrastructure; D011233:Precipitin Tests; D011485:Protein Binding; D011487:Protein Conformation; D015534:Trans-Activators / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D015533:Transcriptional Activation; D029867:Xenopus Proteins; D014982:Xenopus laevis
D003432:Cross-Linking Reagents; D004272:DNA, Mitochondrial; D006609:High Mobility Group Proteins; D009698:Nucleoproteins; D015534:Trans-Activators; C097078:XL-MTTFA protein, Xenopus; D029867:Xenopus Proteins; D005976:Glutaral