Abstract
The human M phase phosphoprotein 1 (MPP1), previously identified through a screening of a subset of proteins specifically phosphorylated at the G2/M transition (Matsumoto-Taniura, N., Pirollet, F., Monroe, R., Gerace, L., and Westendorf, J. M. (1996) Mol. Biol. Cell 7, 1455-1469), is characterized as a plus-end-directed kinesin-related protein. Recombinant MPP1 exhibits in vitro microtubule-binding and microtubule-bundling properties as well as microtubule-stimulated ATPase activity. In gliding experiments using polarity-marked microtubules, MPP1 is a slow molecular motor that moves toward the microtubule plus-end at a 0.07 microm/s speed. In cycling cells, MPP1 localizes mainly to the nuclei in interphase. During mitosis, MPP1 is diffuse throughout the cytoplasm in metaphase and subsequently localizes to the midzone to further concentrate on the midbody. MPP1 suppression by RNA interference induces failure of cell division late in cytokinesis. We conclude that MPP1 is a new mitotic molecular motor required for completion of cytokinesis.
Highlights
Motors, play important roles in cell division
Microtubule dynamics are an intrinsic property of the polymer of tubulin and are highly regulated by the balance of the proteins, and this has been an incentive for the systematic search of mitotic phosphoproteins
We have recently identified a subset of M phase phosphoproteins by expression library screening using the MPM2 monoclonal antibody, which recognizes a phosphoepitope present on a set of 40 –50 proteins that become phosphorylated at the G2/M transition (1, 24 –26)
Summary
Motors, play important roles in cell division. At each stage of mitosis or meiosis, dyneins and various KRPs interact with microtubules in order to ensure centrosome separation, spindle formation and maintenance, chromosome congression, and cytokinesis completion [15,16,17,18,19]. Rounded cells were searched and time lapse Z-sequences were collected as described by Savino et al [38] on a Leica DMIRBE microscope controlled by Metamorph software (Universal Imaging).
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