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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 lqg1p (IQGAP), is the essential light chain for Myo1p, the only type II myosin in S. cerevisiae. However, disruption or reduction of MIc1p-Myo1p inter- action by deleting the Mlc1p binding site on Myo1p or by a point mutation in MLC1, mlc 1-93, did not cause any obvious defect in cytokinesis. In contrast, a different point mutation, mlcl-11, displayed defects in cytokinesis and in interactions with Myo2p and lqg1p. These data suggest that the major function of the Mlc1p-Myo1p interaction is not to regulate Myo1p activity but that Mlc1p may interact with Myo1p, lqg1p, 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. [ABSTRACT FROM AUTHOR]