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XB-ART-16381
EMBO J 1997 Jun 02;1611:3198-206. doi: 10.1093/emboj/16.11.3198.
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The HMG-box mitochondrial transcription factor xl-mtTFA binds DNA as a tetramer to activate bidirectional transcription.

Antoshechkin I , Bogenhagen DF , Mastrangelo IA .


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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.

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Species referenced: Xenopus laevis
Genes referenced: lef1 sox13 sox3 tfam

References [+] :
Alexandrova, Differences between HMG1 proteins isolated from normal and tumour cells. 1987, Pubmed