Regulation of target proteins by small ubiquitin-like modifiers

In this thesis, I aimed at decoding the role of SUMO in the DNA damage repair pathway. The SUMO system is believed to be involved in this process at several levels. I focused on the most inevitable DNA obstacle causing DNA replication stress, and the cellular roles of SUMOylation in repairing DNA replication stress caused DNA damage. Post-translational modifications are essential regulators of proteins. PTMs do not only play their roles solo but extensively interact with each other. Our knowledge about proteins modified by a combination of SUMO and ubiquitin, SUMO and phosphate and crosstalk between them is quite limited. This thesis also aimed at deciphering the crosstalk between SUMOylation and phosphorylation and ubiquitination during the DNA damage response and searching for indirect and direct targets for the human STUbL RNF4, which mediates the ubiquitination of SUMOylated target proteins. Lastly, we adopted the strategy described for SUMO and introduced His10-tagged UFM-1-K0 to identify UFM-1 acceptor lysines. We identified and confirmed RPL26 as a key UFM1 target and further confirmed that the UFMylated form of RPL26 can efficiently interact with the Signal Recognition Particle Receptor, implicating that UFMylation could regulate protein transfer to the Endoplasmic Reticulum. Marie Curie Initial Training Network UPStreamLUMC / Geneeskund