Felicity Watts
Emeritus Professor/Reader

Research

Introduction

Failure to maintain genetic integrity can result in the inheritance of mutations, genetic disorders, cancer or cell death. To ensure genome stability, cells have evolved a number of different ways to deal with DNA damage. These include several DNA repair pathways capable of recognising and repairing different types of damage, and checkpoint mechanisms that arrest the cell cycle to prevent cells from entering the next phase of the cycle with DNA damage or unreplicated chromosomes.

We are interested in a number of DNA damage processes, and how they are coordinated. In particular we are interested in the regulation of protein function through modulation of protein-protein interactions, e.g. through specific modules, such as BRCT domains, or via post-translational modifications, such as ubiquitiylation or sumoylation. 

Dissecting the function of BRCT domains

BRCT (BRCA1-C-terminal) domains, first identified in S. pombe Rad4/Cut5 (Fenech et al 1991) are involved in a range of protein-protein interactions, e.g. Watts & Brisset, 2010. As their name suggests they are present in the BRCA1 protein, mutations in which are responsible for a high proportion of breast and ovarian cancers, and in 53BP1 that binds the tumour suppressor protein p53. BRCT domains generally, but not always, occur inpairs.They are involved in both phosphorylation-dependent and independent interactions. Phosphorylation-dependent interactions usually involve interaction of a phosphorylated protein with a specific phosphoprotein binding site in one of the the BRCT domains within a pair. 

Using fission yeast as a model system, we have investigated the role of the BRCT domains in the S. pombe homologue to 53BP1, Crb2, and the nature of the phosphorylation dependent interaction in which it is involved. Crb2 is a key player in the DNA integrity checkpoint process in S. pombe (Willson et al., 1997). In collaboration with Laurence Pearl's group, we elucidated the structure of the BRCT domains in Crb2 (Kilkenney et al., 2008). Using information gained from this structure we have been analysing the role of the BRCT domains and the proteins with which they interact.

Role of SUMO in maintenance of genetic integrity

Sumoylation can affect protein localisation, enzymatic activity, protein-protein and protein-DNA interactions. It can also target proteins for ubiquitination and subsequent degradation for the proteasome. Through the analysis of mutants defective in sumoylation we have demonstrated that SUMO has multiple roles in maintaining genetic integrity. In addition, we have shown over the last few years, that several DNA replication, recombination and checkpoint proteins are SUMO modified e.g. Rad52 (Ho et al, 2001), Smc6 (Andrews et al, 2005), Rqh1, Mre11 (Watts 2008) and collaboratively that Swi6, Taz1 and Tpz1 are also sumoylated (Shin et al., 2005, Spink et al, 2005, Garg et al, 2014).  We have also analysed the role of sumoylation in meiosis in S. pombe (Spirek et al, 2010)

In the course of our work we also identified two S. pombe SUMO ligases, Nse2 and Pli1 (Andrews et al, 2005). Nse2 is a component of the Smc5/6 complex and is essential for viability. Pli1 is not essential for viability despite having dramatically reduced levels of sumoylation. 

Many other proteins, in addition to those required for genetic integrity, are modified by SUMO or ubiquitin, included in these are translatin initiation factors, e.g. as reviewed in Watts et al 2014. Recently we have identified a number of translation initiation factors, such as eIF4G and eIF4A associated with the Ulp2 SUMO protease, some of which we have demonstrated to be sumoylated (Jongjitwimol et al., 2014). 

Dr Felicity Watts' GDSC Staff Profile http://www.sussex.ac.uk/profiles/2844