Research: My laboratory uses biochemistry in Xenopus egg extracts together with genetic analysis in Caenorhabditis elegans to study mechanisms and pathways that maintain genome stability. Our studies combine different aspects of cell cycle checkpoint control, DNA replication, and DNA damage repair in order to understand how these pathways are integrated so that the complicated task of genome duplication during S phase is performed in an error-free manner. Currently, there are four major areas of interests: 1. Checkpoint-independent control of the cell cycle The last fifteen years have seen enormous progress in the understanding of how DNA damage and replication checkpoint pathways regulate the cell cycle. By contrast, very little is known about checkpoint-independent mechanisms for responding to DNA damage. Work from our laboratory has recently identified a novel damage response pathway that senses the presence of single-strand breaks in DNA and responds through an arrest to further DNA replication. This pathway does not share components with the canonical checkpoint pathway, and thus represents a novel DNA damage response mechanism. We are currently using biochemical purification from frog egg extracts to identify and study the components of this new pathway. 2. Maintenance of stalled replication forks A critical task of the DNA damage checkpoint is to maintain the stability of replication complexes that stall upon exposure to damaged DNA, so that replication may resume after the damage has been repaired or bypassed. We are currently performing genetic screens in C. elegans to identify factors that ensure replication fork stability during the DNA damage response. 3. Regulation of the initiation of DNA replication The initiation of DNA replication is tightly regulated, and this regulation is critical for prevention of genome instability. We have identified a protein, Mus101, which is required for replication initiation and also functions in the DNA damage response. We are currently exploring the mechanism of action of Mus101 in replication, using frog egg extracts. We have found that Mus101 is a component of the pre-replication complex, and that it is recruited to origins of replication through a novel protein activity. We have established a simple assay for Mus101 loading onto origins of replication, and we are now isolating the loading activity using biochemical purification. 4. The role of mutagenic polymerases in generating genotypic variation in response to environmental cues We are interested in the possibility that so-called "trans-lesion" polymerases have evolved for two distinct purposes, DNA repair and the ability to rapidly generate genotypic complexity within a population experiencing environmental stress. We are performing directed evolution experiments in C. elegans to ask if modulating the expression of these polymerases affects the ability of the organism to adapt to changes in the environment.
Selected Publications: W.M. Michael and John Newport. Coupling of mitosis to the completion of S phase through Cdc34-mediated degradation of Wee1. Science 282: 1886-1889 (1998). W.M. Michael, Robert Ott, Ellen Fanning, and John Newport. Activation of the DNA replication checkpoint through RNA synthesis by primase. Science, 289: 2133-2137 (2000). W.M. Michael. Cell cycle: connecting DNA replication to sporulation in Bacillus. Current Biology, 11: R443-445. (2001). Stokes M.P., Van Hatten R., Lindsay H.D., Michael W.M. DNA replication is required for the checkpoint response to damaged DNA in Xenopus egg extracts. J Cell Biol. Sep 2;158(5):863-72. (2002) Van Hatten R.A., Tutter A.V., Holway A.H., Khederian A.M., Walter J.C., Michael W.M. The Xenopus Xmus101 protein is required for the recruitment of Cdc45 to origins of DNA replication. J Cell Biol. 159:541-7 (2002) Stokes M.P., Michael W.M. DNA damage-induced replication arrest in Xenopus egg extracts. J Cell Biol. 163: 245-55 (2003) Stokes M.P., Michael W.M. A novel replication arrest pathway in response to DNA damage. Cell Cycl e 3: 126-7 (2004) |
