Precision to the very end: what happens when two replication forks converge during termination?

点击翻译按钮获取中文摘要

DNA encodes the information that provides the basis for all life. For cell division to take place the entire DNA of a cell has to be fully duplicated, ensuring that both the mother and the daughter cell can get one complete copy. In addition, the copy made has to be identical to the original. Any changes to the DNA can potentially be harmful, as they will alter how cells function, or even lead to cell death. On a single cell level, accuracy of the duplication process is normally so high that not a single error is made when the millions of DNA base pairs are copied. This extraordinary high level of accuracy is achieved by a network of different processes that regulate the duplication process and choreograph segregation of the two complete copies into mother and daughter. However, mutations in the DNA can inactivate this network of processes and it is a hallmark of cancer cells that they grow in an uncontrolled way. We are studying the final stages of the duplication process. Replication of DNA is initiated at specific sites called origins of replication. Two complex machines termed replication forks are recruited to these origins. These replication forks are capable of copying the DNA with high precision. While doing so they move in opposite direction at very high speed until they meet another replication fork coming the opposite way. Our research has revealed that the collision of two fast moving replication forks has the potential to corrupt the DNA and introduce mutations. This cause of mutation is unexpected, because the fusion of two such replication forks is a fundamental process when DNA is copied, and we have identified a number of pathways that can prevent the harmful consequences of fork fusions. Currently we are using the bacterium Escherichia coli to gain a better insight into the mechanics of such fork fusion events. In E. coli only one such fusion event occurs, as the entire DNA is copied by only two replication forks. In our own cells the duplication process is initiated at hundreds of origins, leading to hundreds of fusion events, making studies much more complex. The relative simplicity of fork fusions in E. coli will allow us to study these events at very high detail with many different tools. For example, we will use recently developed microscopy techniques which allow us to directly visualise and track single replication forks inside living cells to study what happens if forks fuse and to identify how these fusion events can cause corruption of the DNA. Our results will allow us to generate a model of how the duplication process of DNA is normally brought to an orderly completion, which will help us to understand this process in our own cells, and our work will reveal whether it might contribute to the development of cancer and ageing.