| Popis: |
The absence of an alternatively spliced exon between the two dsRBMs of dADAR in adult flies results in higher editing activity when compared to the isoform containing the exon seen at earlier stages of development. A number of constructs containing the dsRBMs were successfully cloned and purified. NMR data of RBM1 confirms that the dsRBMs of dADAR are members of the well characterised family of dsRBMs. Each dsRBM has a distinct affinity for dsRNA substrate indicating possible different roles. Point mutations within dsRBM1 result in a loss of binding activity. The self editing site of dADAR is found within exon 7 of the pre-mRNA, 3’ to the second catalytic motif of the deaminase domain. Editing at this site results in a serine to glycine change in the translated protein and has been shown to reduce editing activity in all known substrates. This region of the protein is highly conserved throughout the ADARs and sequence comparisons with human ADAR2 at the DNA level show it has the potential to be edited at the same site as dADAR. My results confirm the hypothesis that the catalytic deaminase domain acquired dsRBMs, increasing the efficiency of the editing reaction on dsRNA. The dsRBMs bind non-specifically to dsRNA altering and stabilising the structure, allowing the catalytic domain easier access to the adenosine nucleoside to be edited. However, because the deaminase domain has activity on its own it too must play a role in binding to dsRNA substrates. The characteristics of a dsRNA substrate do not involve an easily delineated nucleotide sequence but may instead involve a more complex structural motif. This is not recognized by the dsRBMs but by the deaminase domain itself, probably in a way similar to how the ADATs recognize the evolutionary conserved structure of tRNAs. |
