Project description:Editing of mischarged tRNAs by cytoplasmic aminoacyl-tRNA synthetases (aaRSs) is of high significance for protein homeostasis, whose impairment causes neurodegeneration. However, whether mitochondrial translation needs fidelity and the significance of proofreading (editing) by mitochondrial aaRSs are long-term mysteries. Here, we showed that NIH-3T3 cell line critically depend on the editing of mitochondrial threonyl-tRNA synthetase (Tars2) editing, the disruption of which accumulated Ser-tRNAThr and generated a large abundance of Thr-to-Ser misincorporated peptides. Such infidelity impaired mitochondrial translation and oxidative phosphorylation, causing oxidative stress and cell cycle arrest at G0/G1 phase. ROS removal by N-acetylcysteine relieved abnormal cell proliferation.
Project description:The sources of genome instability, a hallmark of cancer, remain incompletely understood. One potential source is DNA re-replication, which arises when the mechanisms that prevent re-initiation of replication origins within a single cell cycle are compromised. Using the budding yeast Saccharomyces cerevisiae, we previously showed that DNA re-replication is extremely potent at inducing gross chromosomal alterations and that this arises in part because of the susceptibility of re-replication forks to break. Here, we examine the ability of DNA re-replication to induce nucleotide level mutations. During normal replication these mutations are restricted by three overlapping error avoidance mechanisms: the nucleotide selectivity of replicative polymerases, their proofreading activity, and mismatch repair. Using lys2InsEA14, a frameshift reporter that is poorly proofread, we show that re-replication induces up to a 30x higher rate of frameshift mutations and that this mutagenesis is due to passage of the re-replication fork, not secondary to re-replication fork breakage. Re-replication can also induce comparable rates of frameshift and base substitution mutations in a more general mutagenesis reporter CAN1, when the proofreading activity of DNA polymerase ε is inactivated. Finally, we show that the induction of lys2InsEA14 frameshift mutations by re-replication is dependent on mismatch repair. These results suggest that the mismatch repair associated with re-replication is attenuated, although at most sequences DNA polymerase proofreading provides enough error correction to mitigate the mutagenic consequences. Thus, re-replication can facilitate nucleotide level mutagenesis in addition to inducing gross chromosomal alterations, broadening its potential role in genome instability.
Project description:As part of an examination of a newly-evolved RNA polymerase ribozyme, 38-6, products of primer extension experiments using an RNA template encoding the hammerhead RNA endonuclease ribozyme, using 38-6 and its less active ancestor 24-3. These products were analyzed by next-generation sequencing to determine the rates of substitution, deletion, and insertion mutations for both polymerases.
