Michael Stark
Professor Emeritus

Research Interests

Analysis of yeast Elongator phosphorylation and its functional consequences

Elongator is a six-subunit protein complex first discovered in yeast but conserved throughout eukaryotes. Although initially proposed to promote efficient transcription, Elongator is now known to be required for addition of 5-methoxycarbonymethyl and 5-carbamoylmethyl modifications to uridine residues in the anticodon wobble position of tRNAs that decode synonymous codons ending in purines (1, 2). These Elongator-dependent wobble uridine modifications enable them to function properly in translation, accounting for the diverse range of phenotypes that are associated with loss of Elongator function. Although nonessential in yeast, deletion of the gene for its largest subunit (Elp1) in mouse is embryonic lethal while mutations in the human Elp1 homologue are responsible for Familial Dysautonomia, a severe recessive neurodevelopmental condition (3). The Elp1 subunit of Elongator is phosphorylated and by studying yeast Elongator in collaboration with the laboratory of Raffael Schaffrath (University of Kassel) we have identified protein kinases and phosphatases that regulate Elongator (4) and sites of phosphorylation on Elp1 that are functionally important. We have recently identified a domain in Elp1 that interacts with tRNA (5) and our current research seeks to understand the role of Elp1 phosphorylation in Elongator function and its relationship to the binding of tRNA by Elp1.
  1. Huang, B., Johansson, M. J. and Bystrom, A. S. (2005). An early step in wobble uridine tRNA modification requires the Elongator complex. RNA 11, 424-436.
  2. Glatt, S., Seraphin, B. and Muller, C. W. (2012). Elongator: transcriptional or translational regulator? Transcription 3, 273-276.
  3. Slaugenhaupt, S.A. and Gusella, J.F. (2002). Familial dysautonomia. Curr. Opin. Genet. Devel. 12, 307-311.
  4. Mehlgarten, C., Jablonowski, D., Breunig, K. D., Stark, M. J. R. and Schaffrath, R.  Elongator function depends on antagonistic regulation by casein kinase Hrr25 and protein phosphatase Sit4. (2009). Mol Microbiol 73, 869-881.
  5. Di Santo, R., Bandau, S. and Stark, M. J. R. (2014). A conserved and essential basic region mediates tRNA binding to the Elp1 subunit of the Saccharomyces cerevisiae Elongator complex. Mol. Microbiol. 92, 1227-1242.
  6. Abdel-Fattah, W. R., Jablonowski, D., Di Santo, R. T. A., Thüring, K. L., Scheidt, V., ten Have, S. M., Helm, M., Schaffrath, R. and Stark, M. J. R. (2015). Phosphorylation of Elp1 by Hrr25 is required for Elongator-dependent tRNA modification in yeast. PLoS Genet 11 (1), e1004931.

The roles of yeast Ipll1 protein kinase in promoting faithful chromosome segregation

Accurate chromosome segregation is vital for maintenance of genome integrity during cell division and the conserved protein kinase Ipl1/Aurora B plays critical roles in ensuring that correct segregation will occur (1). Ipl1/Aurora B promotes chromosome bi-orientation, ensuring that sister chromatids are attached to microtubules from opposite spindle poles so that they are pulled in opposite directions during anaphase (2). Ipl1/AuroraB kinase activity is associated with Sli15 (INCENP), Bir1 (Survivin) and Nbl1 (Borealin) – the Chromosomal Paassenger Complex or CPC – and we have been using the yeast Saccharomyces cerevisae to study how these regulatory subunits control Ipl1 kinase activity during chromosome bi-orientation. We have proposed an explanation for the involvement of Ipl1 in the spindle checkpoint response that delays anaphase chromosome segregation when sister chromatids are not under tension from spindle microtubules (4) and have shown that phosphorylation of Dam1, a key target of Ipl1 at the yeast kinetochore, responds to the tension that results when chromosomes become bi-oriented (5). Our most recent work has examined the role of Sli15 phosphorylation by Ipl1 in CPC function (6).
  1. Carmena, M., Wheelock, M., Funabiki, H. and Earnshaw, W. C.(2012). The chromosomal passenger complex (CPC): from easy rider to the godfather of mitosis. Nat. Rev. Mol. Cell. Biol. 13, 789-803.
  2. Tanaka, T. U., Stark, M. J. R. and Tanaka, K. (2005). Kinetochore capture and bi-orientation on the mitotic spindle. Nature Rev. Mol. Cell Biol. 6, 929-942.
  3. King, E. M. J., Rachidi, N., Morrice, N., Hardwick, K. G. and Stark, M. J. R. (2007). Ipl1p-dependent phosphorylation of Mad3p is required for the spindle checkpoint response to lack of tension at kinetochores. Genes Devel. 21, 1163-1168.
  4. Keating, P., Rachidi, N., Tanaka, T. U. and Stark, M. J. R. (2009). Ipl1-dependent phosphorylation of Dam1 is reduced by tension applied on kinetochores J. Cell Sci. 122, 4375-4382.
  5. Makrantoni, V., Corbishley, S. J., Rachidi, N., Morrice, N. A., Robinson, D. A. and Stark, M. J. R. (2014). Phosphorylation of Sli15 by Ipl1 is important for proper CPC localization and chromosome stability in Saccharomyces cerevisiae. PLoS ONE 9, e89399.
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