Published 25 October 2004. doi:10.1083/jcb.200404045
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 167, Number 2, 315-325
UCS protein Rng3p activates actin filament gliding by fission yeast myosin-II
Matthew Lord1 and
Thomas D. Pollard1,2,3
1 Department of Molecular Cellular and Developmental Biology, Yale University, New Haven, CT 06520
2 Department of Cell Biology, Yale University, New Haven, CT 06520
3 Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520
Correspondence to T. Pollard: thomas.pollard{at}yale.edu
We purified native Myo2p/Cdc4p/Rlc1p (Myo2), the myosin-II motor required for cytokinesis by Schizosaccharomyces pombe. The Myo2p heavy chain associates with two light chains, Cdc4p and Rlc1p. Although crude Myo2 supported gliding motility of actin filaments in vitro, purified Myo2 lacked this activity in spite of retaining full Ca-ATPase activity and partial actin-activated Mg-ATPase activity. Unc45-/Cro1p-/She4p-related (UCS) protein Rng3p restored the full motility and actin-activated Mg-ATPase activity of purified Myo2. The COOH-terminal UCS domain of Rng3p alone restored motility to pure Myo2. Thus, Rng3p contributes directly to the motility activity of native Myo2. Consistent with a role in Myo2 activation, Rng3p colocalizes with Myo2p in the cytokinetic contractile ring. The absence of Rlc1p or mutations in the Myo2p head or Rng3p compromise the in vitro motility of Myo2 and explain the defects in cytokinesis associated with some of these mutations. In contrast, Myo2 with certain temperature-sensitive forms of Cdc4p has normal motility, so these mutations compromise other functions of Cdc4p required for cytokinesis.
Abbreviations used in this paper: ELC, essential light chain; Myo2, Myo2p/Cdc4p/Rlc1p (myosin-II); PI 4, phosphatidylinositol 4; RLC, regulatory light chain; TPR, tetratricopeptide repeat; UCS, Unc45-/Cro1p-/She4p-related.

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