Type I myosins are monomeric motors involved in a range of motile and sensory activities in different cell types. In simple unicellular eukaryotes, motor activity of class I myosins is regulated by phosphorylation of a conserved `TEDS site' residue within the motor domain. The mechanism by which this phosphorylation event affects the cellular function of each myosin I remains unclear. The fission yeast myosin I, Myo1, activates Arp2/3-dependent polymerisation of cortical actin patches and also regulates endocytosis. Using mutants and Myo1-specific antibodies, we show that the phosphorylation of the Myo1 TEDS site (serine 361) plays a crucial role in regulating this protein's dynamic localisation and cellular function. We conclude that although phosphorylation of serine 361 does not affect the ability of this motor protein to promote actin polymerisation, it is required for Myo1 to recruit to sites of endocytosis and function during this process.

rounds of mutagenesis and selection of those sensors with the desired characteristics in a high-throughput (HT) manner i.e. by FACS. However, there is currently no similar HT technology for sorting libraries of fluorescent protein biosensors. Thus, we have developed a novel microfluidic platform designed for high-throughput screening based on FRET change upon analyte binding. Using this platform, we sort a library of fluorescent protein Zn 2þ sensors, selecting for both amount of FRET response and binding affinity for Zn 2þ . The device is shown schematically below. The microfluidic platform incorporates a laser diode-bar optical trap, two-channel fluorescence excitation and detection, and bright-field imaging. This technology has numerous potential applications due to the great versatility in selection parameters and its ability to sort based upon cellular perturbations.