| Popis: |
RNA editing is a programmed change of an RNA sequence that alters the information and/or function found in the gene. Transfer RNA editing often alters the decoding capacity of the tRNA as it alters the anticodon, but often there are also changes from one canonical base to another at a location other than the anticodon. Two types of editing include cytidine to uridine and adenosine to inosine editing. Adenosine to inosine editing in eukaryotes, is known to be performed by an ADAT2 and ADAT3 as a heterodimer, and manages to alter the decoding capacity of a tRNA by base deamination, which alters the wobbling capacity of the tRNA. Less is understood about cytidine to uridine editing. Often this editing is done through the body of the tRNA, sometimes without an obvious function, and no eukaryotic enzymes are known to perform this reaction on tRNAs.In the first study, I will show a new cytidine to uridine tRNA editing event in threonyl-tRNAs that occurs in the nucleus of kinetoplastids on precursor tRNAs with 5’ leader sequence but not 3’ trailers. This is the first example to cytidine to uridine tRNA editing outside of mitochondria. The editing event coincides on a tRNA with adenosine to inosine editing and is found on the same tRNA. In vitro, the presence of uridine enhances adenosine to inosine editing but is not required. In vivo, adenosine to inosine editing is not needed for cytidine to uridine editing.In the second study, I will show that a modification occurs on the same base as the cytidine to uridine editing event in kinetoplastid tRNAThr. Through a series of experiments, I show that there are two modifications at this position, 3-methylcytidine and 3-methyluridine. This is the first example of 3-methyluridne in tRNA and confirms the presence of cytidine to uridine editing of this tRNA. In the third experiment, I will show that ADAT2 and ADAT3, known to perform adenosine to inosine editing in the cytoplasm of the cell, may also perform cytidine to uridine editing in the nucleus of Kinetoplastids. This leads to a variety of potential experiments and very interesting issues to be investigated including how these enzymes may travel from the cytoplasm to nucleus and alter its activity. Lastly I will propose possible biological roles of cytidine to uridine editing and methylation of this tRNA. |
