We study how cells copy their chromosomes before cell division, to ensure that both daughter cells receive a complete copy of the genetic blueprint, which is contained within the chromosomes in DNA. The process of chromosome duplication starts to go wrong in the early development of many human cancers, providing an opportunity to develop new treatments that seek to kill cancer cells without hurting the rest of the body.
Our lab studies a large molecular 'machine' known as the replisome, which is the central player in the process of chromosome duplication. The assembly and disassembly of the replisome is very tightly controlled by phosphorylation and ubiquitylation, to ensure that cells make just one copy of each chromosome before cell division.
Over the last 10 years, much of our work has focussed on replisome disassembly, which we discovered was regulated by coupling ubiquitin to one of the core replisome components. We found that yeast and animal cells use different enzymes to control this process, yet replisome disassembly is controlled in a very similar manner in both cases. Whereas one strand of the DNA duplex at replication forks passes through the centre of the helicase that is at the heart of the replisome, the other parental DNA strand is excluded from the helicase and prevents binding of the ubiquitin ligase to its target site on the replisome until DNA replication termination. In our ongoing research, we study additional enzymes and new pathways that regulate this process in animal cells, either in response to defects in chromosome replication or when cells enter mitosis before genome duplication has been completed.
Most recently, we have started to study the process of replisome assembly during DNA replication initiation in animal cells, based on our identification of an essential assembly factor that is mutated in human disease and is not present in yeasts (where the mechanism of replisome assembly had been studied in most detail until now). Much remains to be learned about this process, and the mechanism of metazoan replisome assembly will be an important focus of our work in the years ahead.
A deeper understanding of replisome assembly and disassembly will help us to understand how cells normally preserve genome integrity, as well as providing new insights into how inherent replication defects in human cancer could be exploited therapeutically.