Molecular insights into primer removal during mtDNA replication

Abstract

Mitochondria are vital for cell survival, and the primary producers of ATP, the energy currency used for various metabolic processes. Mitochondria are unique from other cellular compartments because they have their own genomes of circular small double-stranded DNA (mtDNA) of approximately 16.6 kbp in size. The mtDNA is highly compact, containing no introns and little non-coding DNA. MtDNA has two non-coding regions: one large region known as the control region or the non-coding region that contains the promoters for transcription (LSP and HSP) and the origin of replication of the H strand (OriH), and a smaller region containing the origin of replication for the L-strand (OriL). MtDNA is replicated by a set of replication factors distinct from those needed for DNA replication in the nucleus. A fundamental step in mtDNA replication is the processing of the RNA primers needed for replication initiation.In this thesis, we could demonstrate that Ribonuclease H1 (RNase H1) is essential for the process of replication initiation at OriH. We couldalso elucidate the role of RNase H1 during primer removal and ligation at the mitochondrial origin of light-strand DNA synthesis (OriL) andexplain the pathogenic consequences of disease-causing mutations in RNase H1.These findings have taken the field of mitochondrial DNA transcription and replication forward and generated knowledge to build further research.In the last project, we studied EXOG, a mitochondrial exonuclease. We demonstrated that EXOG could interplay with RNase H1 and other mitochondrial nucleases in vitro and identified a possible pathway for EXOG to function in.