Doctoral defence: Mari Tagel “Finding novel factors affecting the mutation frequency: a case study of tRNA modification enzymes TruA and RluA”

On 29 November at 10:15 Mari Tagel will defend her doctoral thesis “Finding novel factors affecting the mutation frequency: a case study of tRNA modification enzymes TruA and RluA” for obtaining the degree of Doctor of Philosophy (in Molecular Biology).

Supervisors:
Professor Maia Kivisaar, University of Tartu
Professor Emeritus Jaanus Remme, University of Tartu
Research Fellow Heili Ilves, University of Tartu

Opponent:
Dr. Ivan Matic, Institut Cochin (France)

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Summary
Bacteria can live everywhere. To cope with harsh and everchanging environmental conditions there is a constant need for genetic versatility. Mutations are the main source of genetic versatility in bacteria. To understand the evolution and adaptive abilities of bacteria, it is vital to investigate the processes affecting the mutation frequency. We have created, verified, and applied a new test system for detecting factors affecting the mutation frequency in bacteria from the genus Pseudomonas. By exploiting the new assay, we identified several genes affecting the mutation frequency in the soil bacterium Pseudomonas putida, many of which were not previously associated with the mutation frequency. Most surprising finding was that the tRNA modification enzymes TruA and RluA affect mutagenesis. tRNAs are small adaptor molecules that carry the building blocks of enzymes to the ribosome and thus are essential for translation. To improve their performance, tRNAs are extensively modified. Among other roles, modifications help tRNA’s to achieve the correct structure and improve the translation fidelity. TruA and RluA modify U nucleotide into pseudouridines in the close vicinity of tRNA anticodon. We demonstrated that the lack of TruA- and RluA-catalyzed modifications remarkably increases the mutation frequency in P. putida. To further analyze the importance of the modification enzymes TruA and RluA, we measured the stress tolerance, translation fidelity, protein expression and general fitness of P. putida strains lacking TruA or RluA. For comparison we analyzed the phenotypes caused by TruA and RluA deficiency in Pseudomonas aeruginosa and Escherichia coli cells. Our research demonstrates how an enzyme with conserved function can cause diverse phenotypes in different bacteria. Also, the thesis illustrates how the complex world of DNA mutations can be affected by many nonobvious factors.

The defence will be also held in Zoom: https://ut-ee.zoom.us/j/91922663983?pwd=aFFXbGhUSG1zcDh6N1R0TkVjNVJOdz09 (Meeting ID: 919 2266 3983, Passcode: 021155).