Regulation of Yeast Cell Growth and Division

My laboratory is studying molecular mechanisms that regulate growth and division in the budding yeast Saccharomyces cerevisiae, the first eukaryotic organism for which the complete genome sequence became available. A surprisingly large number of fundamental cellular processes are conserved between yeast and higher eukaryotes. The combination of the powerful classical and molecular genetic methodologies available, the well annotated genome and the ability to carry out sophisticated biochemistry and cell biology have turned budding yeast into a valuable model system in which to study conserved regulatory mechanisms. Much of our work is focused on critical roles of protein serine-threonine kinases and phosphatases in the control of yeast cell growth and division. Our approaches include genetics, biochemistry and the direct observation of chromosome behaviour by microscopy.

One area of interest concerns how yeast Ipl1 protein kinase and Glc7 protein phosphatase regulate kinetochore function. Ipl1 is required for promoting bi-orientation of chromosomes on the mitotic spindle, and we want to understand how it fulfils this role. We are currently investigating how three proteins (Sli15, Bir1 and Nbl1) that associate with Ipl1 regulate its activity during chromosome bi-orientation. We are also studying the role of Ipl1 in the checkpoint mechanism that delays anaphase separation of sister chromatids when they are mono-oriented (i.e. not under tension from the spindle microtubules).

A second major focus is on the roles and regulation of Elongator, a highly conserved, six-subunit protein complex. Elongator is required for proper organ development in plants and mutations in the largest subunit (Elp1) of human Elongator are associated with familial dysautonomia, a severe neurodevelopmental disease. Elongator promotes wobble uridine modification in a subset of tRNAs, which is required for them to function efficiently in translation. This process appears to be regulated through phosphorylation of Elp1 and we are investigating the significance of this regulation and identifying the protein kinases and phosphatases that are involved using yeast as a model system.

Mehlgarten, C., Jablonowski, D., Breunig, K. D., Stark, M. J. R. and Schaffrath, R. (2009) Elongator function depends on antagonistic regulation by casein kinase Hrr25 and protein phosphatase Sit4. Mol Microbiol. 79, 869-881.

Keating, P., Rachidi, N., Tanaka, T.U., and Stark, M.J.R., (2009) lpl1-dependent phosphorylation of Dam1 is reduced by tension applied on kinetochores. J Cell Sci 122:4375-4382 View Paper

Makrantoni, V., and Stark, M.J.R., (2009) Efficient chromosome bi-orientation and the tension checkpoint in Saccharomyces cerevisiae both require Bir1p. Mol Cell Biol 29:4552-4562 View Paper

Lain, S., Hollick, J.J., Campbell, J., Staples, O.D., Higgins, M., Aoubala, M., McCarthy, A., Appleyard, V., Murray, K.E., Baker, L., Thompson, A., Mathers, J., Holland, S.J., Stark, M.J., Pass, G., Woods, J., Lane, D.P., Westwood, N.J. (2008) Discovery, in vivo activity, and mechanism of action of a small-molecule p53 activator. Cancer Cell 13:454-463

King, E.M., Rachidi, N., Morrice, N., Hardwick, K.G., Stark, M.J., (2007) IpI1p-dependent phosphorylation of Mad3p is required for the spindle checkpoint response to lack of tension at kinetochores. Genes Devel. 21:1163-1168. View Paper

Fox, G.C., Shafiq, M., Briggs, D.C., Knowles, P.P., Collister, M., Didmon, M.J., Makrantoni, V., Dickinson, R.J., Hanrahan, S., Totty, N., Stark, M.J., Keyse, S.M., McDonald, N.Q. (2007) Redox-mediated substrate recognition by Sdp1 defines a new group of tyrosine phosphates. Nature 447: 487-492. View Paper

Rudolf, J., Makrantoni, V., Ingledew, W.J., Stark, M.J., White, M.F. (2006) The DNA repair helicases XPD and FancJ have essential iron-sulfur domains. Mol. Cell 23:801-808.

Tanaka, T.U., Rachidi, N., Janke, C., Pereira, G., Galova, M., Schiebel, E., Stark, M.J., Nasmyth, K. (2002) Evidence that the IpI1-Sli15 (Aurora kinase-INCENP) complex promotes chromosome bi-orientation by altering kinetochore-spindle pole connections. Cell 108: 317-329.