TY  - THES
T1  - Evidence for an Enzymatic Activity of Exuperantia Necessary for bicoid mRNA Localization
A1  - Wolff,Ines
Y1  - 2012/10/10
N2  - The anterior localization of bicoid mRNA in the Drosophila oocyte is a prerequisite for the establishment of the anterior-posterior axis later in the embryo. Few factors are known to be essential for this process. Aside from swallow, staufen and the ESCRTII, all of which are important for late steps in bicoid mRNA localization, the only early acting factor is exuperantia. Previous work has shown that Exuperantia needs to be present in the nurse cells to promote anterior localization of bicoid mRNA after transport into the oocyte. In exu-mutant flies bicoid mRNA is transported into the oocyte but cannot localize specifically. So far, the molecular function of Exuperantia is not understood and it is unclear how Exuperantia modifies bicoid mRNA in the nurse cells. Previously, two phosphorylation sites in the C-terminal part had been identified, but they are dispensable for Exuperantia's role in bicoid mRNA localization. In addition, an alignment of Exuperantia’s N-terminus with exonucleases was published in 1997, but this finding was not followed up.
Within this thesis a SAM-like domain in the central part of Exuperantia was identified, and there is evidence that this domain might be RNA-binding. Furthermore, the homology to exonucleases was confirmed and a DEDD exonuclease domain (SCOP family c.55.3.5) was characterized in the N-terminus of Exuperantia. Biochemical in-vitro assays with recombinant proteins confirm the importance of these domains and hint at an enzymatic function of Exuperantia.
Using transgenes encoding Venus-tagged proteins, I show that residues, which are known to be essential for the catalytic activity of this family of enzymes, are important in-vivo for Exuperantia's role in bicoid mRNA localization. This suggests that it might be an enzyme with exonuclease activity, which would explain why the protein co-localizes with bicoid mRNA only transiently.
Interestingly, bicoid mRNA itself does not seem to be the target of this enzymatic activity. The transgenes coding for enzymatic inactive proteins described in this thesis can be used as tools and should allow the identification of the in-vivo targets of Exuperantia.
KW  - Exonucleasen
KW  - Drosophila
CY  - Tübingen
PB  - Universitätsbibliothek Tübingen
AD  - Wilhelmstr. 32, 72074 Tübingen
UR  - http://tobias-lib.uni-tuebingen.de/volltexte/2012/6463
ER  -