Monitoring MLCK

Myosin light chain kinase (MLCK) is a busy protein— it phosphorylates myosin's regulatory light chain (and thus activates myosin) during nonmuscle cell contraction, cytokinesis, stress fiber formation, and motility. In general, MLCK is known to be present at the cellular sites implicated in these events, but the results of Chew et al. (page 543) are some of the first hints at the dynamics of that localization and the in situ activity of the kinase.

Chew et al. track MLCK by adding a module with a calcium–calmodulin-binding domain flanked by BFP and GFP. In the absence of calcium, the BFP and GFP are close enough to each other to allow fluorescence resonance energy transfer (FRET) between them. When calcium–calmodulin binds, however, this disrupts FRET. Chew et al. suspect that when there is...