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X–ray structural analysis of the yeast cell cycle regulator Swi6 reveals variations of the ankyrin fold and has implications for Swi6 function

Nature Structural Biology volume 6, pages 157–165 (1999)Cite this article

Abstract

Swi6 is a 92,000 Mr protein common to two distinct transcriptional activation complexes (SBF and MBF) that coordinate gene expression at the G1–S boundary of the yeast cell cycle. The X–ray structure of a central 36,000 Mr fragment has been determined and refined at 2.1 Å resolution. The structure reveals a basic framework of five ankyrin repeat modules that is elaborated through a series of helical insertions distinguishing it from structures of other ankyrin repeat proteins. A second domain contains a ~30–residue region of extended structure that interacts with the ankyrin repeat core over a substantial proportion of its surface. Conservation of residues buried by these interactions indicates that all members of the Swi6/Cdc10 family share a similar architecture. Several temperature–sensitive mutations within Swi6 and Cdc10 appear to disrupt these interdomain contacts rather than destabilize the ankyrin repeat core. The unusual domain arrangement may be crucial for the modulation of interactions with other co–regulatory molecules such as cyclin–CDK complexes, and has implications for the quaternary interactions within the multisubunit SBF and MBF transcription complexes.

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Figure 1: a, Schematic representation of the protein components and DNA–binding specificity of the SBF and MBF complexes.
Figure 2: a, Final SIGMAA–weighted 2Fo – Fc 'omit' density for the region of the molecule around the ANK V β–hairpin contoured at 1.0σ.
Figure 3: a, The structure of the Swi6–36kD fragment.
Figure 4: Sequence homology between seven members of the Swi6/Cdc10 family within the ANK region.
Figure 5: a, Contacts between the AAD and the upper surface of the ANK core.
Figure 6: B–factor distribution in the refined structure.
Figure 7: a, The location of previously identifed ts mutations of Cdc10 in green56 and Swi6 in yellow55 mapped onto the Swi6–36kD structure.

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Acknowledgements

We thank S. Gamblin for invaluable help with crystal handling and data collection, X. Bing for initial crystallization experiments, A. Gonzales for assistance with the MAD experiment, and G. Dodson, S. Gamblin and K. Rittinger and for critical evaluation of the manuscript. Finally we are grateful to N. Pavletich and R. Marmorstein for coordinates provided prior to general release.

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  1. Division of Protein Structure, Mill Hill, The Ridgeway, London, NW7 1AA, UK

    Rachel Foord, Ian A. Taylor & Stephen J. Smerdon

  2. Division of Yeast Genetics, National Institute for Medical Research, Mill Hill, The Ridgeway, London, NW7 1AA, UK

    Steven G. Sedgwick

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Foord, R., Taylor, I., Sedgwick, S. et al. X–ray structural analysis of the yeast cell cycle regulator Swi6 reveals variations of the ankyrin fold and has implications for Swi6 function. Nat Struct Mol Biol 6, 157–165 (1999). https://doi.org/10.1038/5845

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