tRNA修飾ランドスケープが新規タンパク質機能の進化に与える影響

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Out of the three aims of the proposed research, I completed Aim 1 successfully and published the results. Work on Aims 2 and 3 is still ongoing.In Aim 1, we studied the function of the tRNA modification m1G37 in bacteria. This modification, introduced by the tRNA methyltransferase TrmD, is thought to be essential for growth in bacteria because it prevents frameshift errors that have a deleterious effect on protein function. However, many other tRNA modifications have a similar role in preventing frameshift errors, so it was unclear why m1G37 is particularly essential. To address this question, we performed an evolutionary repair experiment, studying the evolutionary adaptation of Escherichia coli to mutations in the trmD gene. Surprisingly, the mutant bacteria showed slow growth even if m1G37 was completely abolished, and showed almost full recovery of growth after several weeks of evolution. Whole-genome sequencing showed that this was achieved mainly through duplication and mutation of the gene proS, which is responsible for aminoacylation of proline tRNA. This suggested that the main function of m1G37 is related to aminoacylation rather than mistranslation, which we confirmed using biochemical and growth assays. These results provide further evidence that bacteria have a high tolerance for protein mistranslation, show that evolutionary repair can reveal hidden functions of essential genes, and have implications for development of antibiotics targeting trmD