The amino terminal extension of mammalian mitochondrial RNA polymerase ensures promoter specific transcription initiation.
Mammalian mitochondrial transcription is executed by a single subunit mitochondrial RNA polymerase (Polrmt) and its two accessory factors, mitochondrial transcription factors A and B2 (Tfam and Tfb2m). Polrmt is structurally related to single-subunit phage RNA polymerases, but it also contains a unique N-terminal extension (NTE) of unknown function. We here demonstrate that the NTE functions together with Tfam to ensure promoter-specific transcription. When the NTE is deleted, Polrmt can initiate transcription in the absence of Tfam, both from promoters and non-specific DNA sequences. Additionally, when in presence of Tfam and a mitochondrial promoter, the NTE-deleted mutant has an even higher transcription activity than wild-type polymerase, indicating that the NTE functions as an inhibitory domain. Our studies lead to a model according to which Tfam specifically recruits wild-type Polrmt to promoter sequences, relieving the inhibitory effect of the NTE, as a first step in transcription initiation. In the second step, Tfb2m is recruited into the complex and transcription is initiated.
Department of Medical Biochemistry and Cell Biology, University of Gothenburg, PO Box 440, Gothenburg, Sweden, Department of Chemical and Biological Engineering/Physical Chemistry, Chalmers University of Technology, S-41296 Gothenburg, Sweden, Department of Cell and Molecular Biology, Karolinska Institutet, S-171 77 Stockholm, Sweden, Department of Laboratory Medicine, Karolinska Institutet, SE-17177 Stockholm, Sweden, Max Planck Institute for Biology of Ageing, Gleueler Str. 50 a D-50931 Cologne, Germany, Centre for Structural Systems Biology, DESY-Campus, D-22603 Hamburg, Germany and European Molecular Biology Laboratory, Hamburg Unit, 22603 Hamburg, Germany.
Viktor
V
Posse
Emily
E
Hoberg
Anke
A
Dierckx
Saba
S
Shahzad
Camilla
C
Koolmeister
Nils-Göran
NG
Larsson
L Marcus
LM
Wilhelmsson
B Martin
BM
Hällberg
Claes M
CM
Gustafsson
D000818:Animals; D004268:DNA-Binding Proteins / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006609:High Mobility Group Proteins / Q000378:metabolism; D006801:Humans; D008780:Methyltransferases / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000235:genetics; D024101:Mitochondrial Proteins / Q000378:metabolism; D009154:Mutation; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000378:metabolism; D061785:Transcription Initiation, Genetic
D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D024101:Mitochondrial Proteins; C081930:Tfam protein, mouse; D014157:Transcription Factors; D008780:Methyltransferases; C462443:TFB2M protein, human; D012321:DNA-Directed RNA Polymerases; C519567:POLRMT protein, human; C000588975:Polrmt protein, mouse