A model for transcription initiation in human mitochondria

Abstract

Regulation of transcription of mtDNA is thought to be crucial for maintenance of redox potential and vitality of the cell but is poorly understood at the molecular level. In this study we mapped the binding sites of the core transcription initiation factors TFAM and TFB2M on human mitochondrial RNA polymerase, and interactions of the latter with promoter DNA. This allowed us to construct a detailed structural model, which displays a remarkable level of interaction between the components of the initiation complex (IC). The architecture of the mitochondrial IC suggests mechanisms of promoter binding and recognition that are distinct from the mechanisms found in RNAPs operating in all domains of life, and illuminates strategies of transcription regulation developed at the very early stages of evolution of gene expression.

Structural models of mammalian mitochondrial transcription factor B2

“…This means that model 2 in which the Nterminus is in proximity to +2/+3 sites of the promoter is the most probable model. Model 2 also agrees with a recently published biochemical study [67]. In that study the region encompassing residues 315-352 of the C-terminal domain of TFB2M was mapped to interact with residues 588-604 in POLRMT; which is consistent with model 2.…”

“…The structural models suggest a nucleic acid binding site consisting of the cleft between the N-and C-terminal domains and a basic surface of the N-terminal domain. Residues in this site have been shown recently to be essential for transcription [67]. We speculate that this binding site may be used by TFB2M to promote formation of the open complex and/or to stabilize it as suggested by studies of the yeast protein [23].…”

Maintenance and Expression of Mammalian Mitochondrial DNA

“…−50 to −60 (48). This interaction is also evident from cross-linking experiments that have demonstrated direct contacts between POLRMT and the upstream promoter region (50). The contacts formed are explained from structural data demonstrating that TFAM induces a sharp bend in the promoter DNA, which helps to juxtapose POLRMT and the −50 to −60 region (39,40).…”

Mechanism of Transcription Anti-termination in Human Mitochondria

“…In the absence of a dedicated mitochondrial primase, replication primers are generated by the mitochondrial RNA polymerase (mtRNAP), a single subunit enzyme that resembles phage RNAPs (Gustafsson et al, 2016; Phillips et al, 2017; Ringel et al, 2011; Wanrooij et al, 2008). The early replication events in human mitochondria require assembly of the transcription initiation complex at the light strand promoter (LSP) (Morozov et al, 2015) and termination of transcription after synthesis of a ∼120 nt RNA transcript to produce the primer necessary to initiate mtDNA synthesis (Chang and Clayton, 1985). This termination event is triggered by a conserved G-rich sequence, called CSBII, which is located near the replication origin OriH and encodes a short G-quadruplex structure (Wanrooij et al, 2012; Wanrooij et al, 2010).…”