"Wobble uridine modifications in mammalian tRNA - biogenesis and function"

The human genome consists of DNA and contains thousands of genes that provide the recipes for proteins. In a process denoted translation, the information from DNA is translated into protein, which is a chain of amino acids. Central in this process is a group of molecules called tRNAs (transfer RNAs). The tRNAs consist of four building blocks, abbreviated A, C, G, and U, and are subject to further biochemical modifications. The most common of these is methylation, catalysed by specific enzymes, so-called methyltransferases. Within this project, we have studied enzymes that modify tRNAs and proteins that are involved in the process of translation. We have been part of a study showing that the so-called Elongator complex plays an important part in the formation of certain tRNA modifications (Lin et al. PLoS Genetics, 2013), and we have also studied another tRNA modifying enzyme ALKBH8 (Zdzalik et al., PLoS ONE, 2014).

Mammals have nine different homologues (ALKBH) of the DNA repair demethylase AlkB from E. coli. We have recently, for the first time, demonstrated a non-repair function for an ALKBH protein. We found that ALKBH8 is a bifunctional tRNA modification enzyme with both methylase and hydroxylase activities, involved in the formation of modified uridines in the wobble position. It was revealed that mammalian tRNA contains two novel wobble uridine modifications, (S)- and (R)-mchm5U, and that the ALKBH8 methylase is required for their formation, while the ALKBH8 hydroxylase performs the last step in (S)-mchm5U biosynthesis. Mammalian wobble uridine modifications and their formation have been the subject of only a few studies, and, through our work on the ALKBH8 f unction, we have acquired knowledge and experience in studying tRNA modifications in mammalian cells. Thus, in the proposed project we aim to further elucidate the mechanisms by which mammalian wobble uridine modifications are formed, and we will also stu dy the role of such modifications in accurate and efficient decoding during protein translation.