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Reversible phosphorylation of myosin regulatory light chain (MRLC) is a key regulatory mechanism controlling myosin activity, and thus regulating the actin/myosin cytoskeleton. In a recent paper in Molecular Biology of the Cell (Vereshchagina, N., Bennett, D., Kirchner, J., Szöör, B., White-Cooper, H. and Alphey, L. [2004] Mol. Biol. Cell, 15: 4395-4405) we showed that PP1Β, a specific isoform of Serine/Threonine Protein Phosphatase 1 (PP1), regulates non-muscle myosin in Drosophila and that this is the essential role of PP1Β. Loss of PP1Β leads to increased levels of phosphorylated non-muscle MRLC (Sqh) and actin disorganisation; these phenotypes can be suppressed by reducing the amount of active myosin. The cover image shows a confocal micrograph of a small clone of PP1Β mutant Drosophila ovarian follicle cells (marked by lack of EGFP, green), which have accumulated high levels of phosphorylated myosin regulatory light chain, Sqh (red). PP1Β, together with its proposed specific substrate and regulatory proteins, are all highly conserved between flies and humans, suggesting that this role may be conserved. The confocal image was generated by Natasha Vereshchagina and Helen White-Cooper.