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Fox Lung Cells with mRuby-Light Chain Myosin

Cultured fox lung fibroblasts (FoLu line) appear in this digital video sequence expressing a red fluorescent protein tag fused to light chain myosin. The myosin regulatory light chain (RLC) in smooth muscle tissues and nonmuscle cells is critical in the increase of actin-activated myosin MgATPase activity and initiates smooth muscle contraction. Myosin light chain kinases (MLCK) catalyze phosphate transfer from MgATP to a serine residue located by the N-terminal of myosin RLCs. The vertebrate forms of MLCK are dependent on calcium/calmodulin for activity with an inherent activation constant equal to 1 nanometer.

The fluorescent protein employed to visualize light chain myosin, mRuby, is a derivative of eqFP611, a far-red fluorescent protein isolated from the bubble-tip anemone (Entacmaea quadricolor). mRuby is monomeric, bright, and possesses a large Stokes shift. Excitation and emission maxima of mRuby occur at 558 and 605 nanometers, respectively.