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Journal Article

The amino terminal extension of mammalian mitochondrial RNA polymerase ensures promoter specific transcription initiation

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Larsson, Nils-Göran
Mitochondrial Biology, Department Larsson, Max Planck Institute for Biology of Ageing, Max Planck Society;

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Citation

Posse, V., Hoberg, E., Dierckx, A., Shahzad, S., Koolmeister, C., Larsson, N.-G., et al. (2014). The amino terminal extension of mammalian mitochondrial RNA polymerase ensures promoter specific transcription initiation. NUCLEIC ACIDS RESEARCH, 42(6), 3638-3647. doi:10.1093/nar/gkt1397.

Abstract

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.