Post-transcriptional modifications and regulation of mRNAs in human mitochondria.

Abstract

Mitochondria contain their own circular genome (mtDNA), which encodes essential components of the oxidative phosphorylation (OXPHOS) system. Mitochondrial DNA transcription is a unique and relatively simple process, requiring a specialized transcription machinery that consists of a RNA polymerase (POLRMT), two transcription factors (TFAM and TFB2M), and an elongation factor (TEFM). During transcription, a non-canonical initiating nucleotide (NCIN) can be incorporated as the first nucleotide, serving as a 5' cap. Mitochondrial transcription produces large polycistronic transcripts, which are subsequently processed by ribonucleases to generate individual messenger RNAs (mt-mRNAs), ribosomal RNAs (mt-rRNAs), and transfer RNAs (mt-tRNAs). This review will specifically focus on the maturation and regulation of mt-mRNAs. Following their release from the primary transcript, mt-mRNAs undergo various post-transcriptional modifications, including methylation, pseudouridylation, and polyadenylation. These modifications play a crucial role in determining mt-mRNAs fate by influencing their stability, translation efficiency, and overall mitochondrial function. Additionally, the spatial organization of these processes within mitochondrial RNA granules (MRGs) suggests a compartmentalized system for mitochondrial gene regulation, ensuring precise coordination between transcription, processing, and translation. A deeper understanding of these post-transcriptional modifications provides valuable insights into mitochondrial gene expression and its broader impact on cellular metabolism.