Molecular mechanisms and cellular functions of RNA methyltransferases targeting non-coding RNAs

by Nicole Kleiber
Cumulative thesis
Date of Examination:2024-08-22
Date of issue:2024-12-23
Advisor:Prof. Dr. Markus Bohnsack
Referee:Prof. Dr. Markus Bohnsack
Referee:Prof. Dr. Claudia Höbartner
Referee:Prof. Dr. Peter Rehling
Referee:Prof. Dr. Argyris Papantonis
Referee:Prof. Dr. Ralf Ficner
Referee:Dr. Sonja Lorenz
Persistent Address: http://dx.doi.org/10.53846/goediss-10975

 

 

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Abstract

English

Cellular RNAs contain diverse modified nucleotides that regulate their structure, stability, biogenesis and molecular functions. In abundant non-coding RNAs such as ribosomal (r)RNAs, transfer (t)RNAs and small nuclear (sn)RNAs, modifications cluster in functionally important regions of the RNA and contribute to the modulation of gene expression. The relevance of these modifications is emphasised by diverse pathologies arising due to dysregulation of the levels of RNA modifications or of the proteins that install them. The identification and characterisation of the enzymes responsible for installing modified nucleotides is an important turning point in elucidating modification functions. This study focused on the characterisation of specific RNA methyltransferases, the mechanisms by which they catalyse formation of specific methylation marks and the investigation of the impact these modifications have on cellular functions associated with the substrate RNAs. Here, METTL8 was identified as an RNA methyltransferase that introduces m3C32 modifications in mitochondrial (mt-)tRNAsThr/Ser(UCN) and the presence of these modifications was found to modulate the structure of the anticodon stem loop (ASL) to allow for optimal mitochondrial translation. TRMT11 and THUMPD3 install m2G modifications in positions 10 and 6/7 of several nuclear-encoded tRNAs and these modifications were shown to collectively regulate cell proliferation and cytoplasmic translation, without affecting folding or aminoacylation of these tRNAs. Lastly, THUMPD2 is an m2G methyltransferase that modifies the U6 snRNA in position 72 and absence of the m2G72 modification leads to perturbations in alternative splicing. The stage of U6 biogenesis when this modification is installed and the mechanisms of target recognition by THUMPD2 were dissected.
Keywords: RNA modifications; RNA methyltransferases; METTL8; THUMPD2; 3-methylcytidine; N2-methylguanosine; modifications in tRNAs; modifications in snRNAs