Figure 1

Cytoskeletal filament nucleation by modified subunits. (a) Nucleation of actin filaments by the Arp2/3 complex. Left: diagram of Arp2/3 complex before and after activation, showing rearrangement of actin-like subunits leading to templated filament growth (Copyright 2008 from Molecular Biology of the Cell, 5th edition by Alberts et al. Reproduced by permission of Garland Science/Taylor & Francis LLC [41]). Right: electron micrograph showing the appearance of an actin filament nucleated by Arp2/3 (at the bottom) (from Proc Natl Acad Sci U S A[35]). (b) Nucleation of microtubules by the γ-tubulin ring complex. Left: diagram of microtubule templated from a ring complex (Copyright 2008 from Molecular Biology of the Cell, 5th edition by Alberts et al. Reproduced by permission of Garland Science/Taylor & Francis LLC [41]). Middle, structure of the ring complex by cryo-electron microscopy, showing how the γ-tubulins are held in the proper configuration to imitate a microtubule plus end (reprinted by permission from Macmillan Publishers Ltd: Nat Rev Mol Cell Biol 12:709–721, copyright 2011 [38]). Right, electron micrograph of the end of a microtubule nucleated from a ring complex (reprinted by permission from Macmillan Publishers Ltd: Nat Cell Biol 2:365–370, copyright 2000 [42]).