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广东快乐十分钟开奖走势图:Watching microtubules grow one tubulin at a time
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Microtubules are mesoscale dynamic noncovalent polymers essential for all eukaryotic life. Their dynamic behavior is crucial for cells to divide, differentiate, and migrate. Microtubules are built through the lateral assembly of linear protofilaments formed through the head-to-tail association of tubulin dimers (1). Lateral association of protofilaments forms the hollow cylindrical microtubule. Microtubules grow through the addition of tubulin dimers at their tips. Observations of individual microtubules using a variety of optical techniques coupled with biochemical analyses and modeling have resulted in a conceptual framework to understand the kinetics and structural transitions that occur during their growth and disassembly. In PNAS, Mickolajczyk et al. (2) harness the power of recent developments in recombinant tubulin engineering (3??–6) and interferometric scattering microscopy (iSCAT) (7) to measure directly the association and dissociation constants of single tubulin dimers at the growing microtubule tip (kOn and kOff, respectively) and advance a model for microtubule growth.
Despite decades of research on microtubule dynamics, basic polymer properties such as rates of tubulin dimer addition and loss at microtubule tips are still controversial and vary by an order of magnitude between studies, even in a simplified in vitro system (1, 8, 9). These uncertainties limit our understanding of tubulin self-assembly and its regulation by the myriad of proteins that associate with microtubules in cells (10). Why do we still lack a detailed view of microtubule assembly when similar efforts in the actin field have yielded a deeper quantitative understanding of actin dynamics (11)? One reason is the multistranded structure of the microtubule. Unlike actin, which consists of two helical strands, microtubules are typically formed by 13 protofilaments that can grow independently from each other. Multiple protofilaments can create different arrangements that can give rise to different association and dissociation kinetics …
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