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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]

Myo4p is a nonessential type V myosin required for the bud tip localization of ASH1and IST2 mRNA. These mRNAs associate with Myo4p via the She2p and She3p proteins. She3p is an adaptor protein that links Myo4p to its cargo. She2p binds to ASH1 and 1ST2 mRNA, while She3p binds to both She2p and Myo4p. Here we show that Myo4p and She3p, but not She2p, are required for the inheritance of cortical ER in the budding yeast Saccharomyces cerevisiae. Consistent with this observation, we find that cortical ER inheritance is independent of mRNA transport. Cortical ER is a dynamic network that forms cytoplasmic tubular connections to the nuclear envelope. ER tubules failed to grow when actin polymerization was blocked with the drug latrunculin A (Lat-A). Additionally, a reduction in the number of cytoplasmic ER tubules was observed in Lat-A--treated and myo44 cells. Our results suggest that Myo4p and She3p facilitate the growth and orientation of ER tubules. [ABSTRACT FROM AUTHOR]