Project description:The abundant RNA modification pseudouridine (Ψ) has been mapped transcriptome-wide by chemically modifying pseudouridines with carbodiimide and detecting the resulting reverse transcription stops in high-throughput sequencing. However, these methods have limited sensitivity and specificity, in part due to the use of reverse transcription stops. We sought to use mutations rather than just stops in sequencing data to identify pseudouridine sites. Here, we identify reverse transcription conditions that allow read-through of carbodiimide-modified pseudouridine (CMC-Ψ), and we show that pseudouridines in carbodiimide-treated human ribosomal RNA have context-dependent mutation and stop rates in high-throughput sequencing libraries prepared under these conditions. Furthermore, accounting for the context-dependence of mutation and stop rates can enhance the detection of pseudouridine sites. Similar approaches could contribute to the sequencing-based detection of many RNA modifications.
Project description:The spontaneous mutation rate is a crucial parameter in molecular evolution which is maintained very low. To better characterize how proofreading activity of the DNA polymerase and Mismatch repair (MMR) which are ubiquitous in all kingdoms of life shape a mutational landscape we built B. subtilis 168-derived strains allowing conditional inactivation of either one or both of these two error reparation mechanisms. In practice, we used an IPTG-inducible promoter to control the expression of mutant alleles selected for their ability to displace by competition their functional counterparts. The first allele, denoted here mutL*, has a mutation in the ATP hydrolysis active site of MutL. The second allele, denoted here polC* encodes an exonuclease-deficient variant of PolC. Fluctuation tests and Mutation Accumulation experiments confirmed extremely high mutation rates, upon IPTG-induction, in the strain that combine these two deficient alleles in a synthetic operon (mutL*//polC*). The purpose of this transcritomic study was to better characterize this inducible system. Analysis of the data did not reveal specific transcriptional responses of the bacterium to IPTG addition and extreme mutations rates.
