Mitochondria have their own genome which encodes oxidative phosphorylation (OXPHOS) related genes, tRNAs and mitochondrial ribosomal RNAs. The single-subunit RNA polymerase, POLRTM, is responsible for the transcription of mitochondrial coded genes. Similar to the nuclear RNA polymerase II, transcription processes of POLRMT are controlled by transcription factors. Transcription Elongation Factor of Mitochondria (TEFM) enhances transcription elongation process of human POLRMT and facilitates POLRMT transcription at oxidative damaged DNA sites as well as CSBII, a conserved sequence element related to the switching between mitochondrial DNA replication and transcription. However, the mechanism how TEFM modulates POLRMT transcription elongation dynamics remains unknown. Therefore, we perform...[ Read more ]

Mitochondria have their own genome which encodes oxidative phosphorylation (OXPHOS) related genes, tRNAs and mitochondrial ribosomal RNAs. The single-subunit RNA polymerase, POLRTM, is responsible for the transcription of mitochondrial coded genes. Similar to the nuclear RNA polymerase II, transcription processes of POLRMT are controlled by transcription factors. Transcription Elongation Factor of Mitochondria (TEFM) enhances transcription elongation process of human POLRMT and facilitates POLRMT transcription at oxidative damaged DNA sites as well as CSBII, a conserved sequence element related to the switching between mitochondrial DNA replication and transcription. However, the mechanism how TEFM modulates POLRMT transcription elongation dynamics remains unknown. Therefore, we performed single-molecule optical tweezers assay of POLRMT transcription elongation. We found that TEFM does not change pause-free translocation of POLRMT but enhances POLRMT transcription elongation by reducing the pause frequency and shortening the pause durations of long-lifetime pauses. Furthermore, our real-time observation of POLRMT transcription shows that TEFM inhibits transcription pre-termination by preventing G-quadruplex formation at CSBII sequence. This indicates TEFM regulates DNA replication and transcription switch in mitochondria. These findings elucidate the general function of TEFM on transcription elongation dynamics and help to understand how transcription and DNA replication switch is controlled at the CSBII sequence.

Key words: Mitochondrial RNA Polymerase, Transcription Elongation, Optical Tweezers, Transcription Elongation Factor, TEFM, Conserved sequence block II, G-quadruplex