PhD defence S.R. (Susanne) Brükner

Brief summary of the doctoral thesis:

Functional life is dependent on the integrity of the organism’s genome. One major player in the maintenance of genomic stability is the process of DNA mismatch repair (MMR) which enhances replication fidelity. Following the DNA replication, this machinery scans the newly synthetized DNA for wrongly inserted bases and initiates their repair if necessary. The importance of this process is highlighted by the fact that the sequence of MMR events and most of its protein components are conserved in all kingdoms of life.

The E. coli MMR proteins have long served as model system to elucidate the pathway. Over the years, a plethora of data have been assembled, and especially the initial steps of E. coli MMR are well understood in molecular detail. However, when it comes to the actions of MutL - the second protein in the MMR cascade - many aspects remain poorly understood. Through the work presented in this thesis, I added another piece to this puzzle.

The human MMR proteins are even more difficult to study than their bacterial counterparts, partly because they are difficult to produce recombinantly and have hence not been wellcharacterized in vitro. By establishing a robust protocol for the recombinant production of human MutSα, I paved the way for hopefully many more in vitro studies in human MMR. In two such studies, I showed that not all findings from E. coli can be translated to the human proteins, and that it is worth studying them in detail.

With the work in this thesis I provide further understanding of the MMR proteins, their interactions and regulation in both E. coli and human. My findings demonstrate that, although the MMR machinery is highly complex and flexible, seemingly miniscule altercations to individual components can have far-reaching effects on an organism over time. Therefore, it will be worthwhile to pay attention to details, especially in a time where longevity of the human population is becoming a major focus in our society.