Biology subjects

Zamudio-Ochoa, A.

Publications and source records attributed to Zamudio-Ochoa, A..

3 recordsLinked to original sources

bioRxiv2025

Structural Basis for Promoter Recognition and Transcription Factor Binding and Release in Human Mitochondria

Transcription in human mitochondria is driven by a core apparatus consisting of a Pol A family RNA polymerase (mtRNAP), the initiation factors TFAM and TFB2M, and the elongation factor TEFM. While earlier structures of initiation and elongation complexes provided valuable snapshots, they represent isolated stages of a highly dynamic and multistep process. Critical aspects of mitochondrial transcription--such as DNA recognition and melting, promoter escape, and the release of initiation factors--remain poorly understood. Here, we present a series of cryo-EM structures that capture the transcription complex as it transitions from the initial open promoter complex to the processive elongation complex through intermediate stages. Our data reveal new determinants of promoter specificity, the sequential disengagement of mtRNAP from TFAM and the promoter, the release of TFB2M, and the recruitment of TEFM. Together, these findings provide a detailed molecular mechanism underlying transcription in human mitochondria.

molecular biology↗

bioRxiv2024

Insights into the Translational Activation Mechanisms of the COX1 mRNA in Yeast Mitochondria

Mitochondrial translation is a critical regulatory step in mitochondrial genome expression. In Saccharomyces cerevisiae, translational activators are believed to bind to the 5 UTRs of their target mRNAs to position the mitochondrial ribosome at the start codon. Pet309 and Mss51 are translational activators of COX1 mRNA, which encodes subunit one of cytochrome c oxidase. Pet309 physically interacts with COX1 mRNA, but no direct interaction of Mss51 with its target mRNA has been detected. Currently, the mechanisms underlying translational activation of COX1, or any other mitochondrial gene, remain poorly understood. To explore in depth the mechanism of COX1 mRNA translational activation, we studied the association of Pet309 and Mss51 with the mitochondrial ribosome. Both Pet309 and Mss51 interact with the mitoribosome regardless of the presence of COX1 mRNA or of each other. Pet309s association with the ribosome and with COX1 mRNA depends on its N-terminal domain. These findings indicate that Pet309 and Mss51 stably interact with the mitoribosome independently of an active translation. By integrating our data with previously published research, we propose a new mechanism of COX1 mRNA translation activation. SUMMARY STATEMENTYeast mitochondrial mRNAs require translational activators by an almost unknown mechanism. Based on our findings on Mss51 and Pet309 function, we present a new model for translation of the COX1 mRNA

molecular biology↗

bioRxiv2023

Molecular Basis for Maternal Inheritance of Human Mitochondrial DNA

Uniparental inheritance of mitochondrial DNA (mtDNA) is an evolutionary trait found in nearly all eukaryotes. In many species, including humans, the sperm mitochondria are introduced to the oocyte during fertilization1, 2. The mechanisms hypothesized to prevent paternal mtDNA transmission include ubiquitination of the sperm mitochondria and mitophagy3, 4. However, whether these mechanisms play a decisive role in paternal mtDNA elimination has been disputed5, 6. We found that mitochondria in human spermatozoa are devoid of mtDNA and lack mitochondrial transcription factor A (TFAM), the major nucleoid protein required to protect, maintain, and transcribe mtDNA. During spermatogenesis, sperm cells express an isoform of TFAM, which retains the mitochondrial pre-sequence, ordinarily removed upon mitochondrial import. Phosphorylation of this pre-sequence prevents mitochondrial import and directs TFAM to the spermatozoon nucleus. TFAM re-localization from the mitochondria of spermatogonia to the spermatozoa nucleus directly correlates with the elimination of mitochondrial DNA, thereby explaining maternal inheritance in this species.

molecular biology↗