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The HMG‐box mitochondrial transcription factor xl‐mtTFA binds DNA as a tetramer to activate bidirectional transcription
Author(s) -
Antoshechkin Igor,
Bogenhagen Daniel F.,
Mastrangelo Iris A.
Publication year - 1997
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/16.11.3198
Subject(s) - biology , transcription factor , mitochondrial dna , transcription (linguistics) , tfam , tetramer , dna , dna binding protein , hmg box , microbiology and biotechnology , genetics , gene , biochemistry , enzyme , linguistics , philosophy
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.