Published 21 June 2004. doi:10.1083/jcb.200401040
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 165, Number 6, 843-855
Identification and functional analysis of the essential and regulatory light chains of the only type II myosin Myo1p in Saccharomyces cerevisiae
Jianying Luo1,
Elizabeth A. Vallen2,
Christopher Dravis1,
Serguei E. Tcheperegine1,
Becky Drees3, and
Erfei Bi1
1 Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
2 Department of Biology, Swarthmore College, Swarthmore, PA 19081
3 Department of Genetics and Medicine, University of Washington, Seattle, WA 98195
Address correspondence to Erfei Bi, Dept. of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6058. Tel.: (215) 573-6676. Fax: (215) 898-9871. email: ebi{at}mail.med.upenn.edu
Cytokinesis in Saccharomyces cerevisiae involves coordination between actomyosin ring contraction and septum formation and/or targeted membrane deposition. We show that Mlc1p, a light chain for Myo2p (type V myosin) and Iqg1p (IQGAP), is the essential light chain for Myo1p, the only type II myosin in S. cerevisiae. However, disruption or reduction of Mlc1pMyo1p interaction by deleting the Mlc1p binding site on Myo1p or by a point mutation in MLC1, mlc1-93, did not cause any obvious defect in cytokinesis. In contrast, a different point mutation, mlc1-11, displayed defects in cytokinesis and in interactions with Myo2p and Iqg1p. These data suggest that the major function of the Mlc1pMyo1p interaction is not to regulate Myo1p activity but that Mlc1p may interact with Myo1p, Iqg1p, and Myo2p to coordinate actin ring formation and targeted membrane deposition during cytokinesis. We also identify Mlc2p as the regulatory light chain for Myo1p and demonstrate its role in Myo1p ring disassembly, a function likely conserved among eukaryotes.
Key Words: septins; Myo2p; Myo4p; cytokinesis; actomyosin ring
Abbreviations used in this paper: coIP, coimmunoprecipitation; DIC, differential interference contrast; ELC, essential light chain; RLC, regulatory light chain; SC, synthetic complete.

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