@article{floyd_molines_lei_honts_chang_elting_vaikuntanathan_dinner_bhamla_2023, title={A unified model for the dynamics of ATP-independent ultrafast contraction}, volume={120}, ISSN={["1091-6490"]}, DOI={10.1073/pnas.2217737120}, abstractNote={In nature, several ciliated protists possess the remarkable ability to execute ultrafast motions using protein assemblies called myonemes, which contract in response to Ca2+ ions. Existing theories, such as actomyosin contractility and macroscopic biomechanical latches, do not adequately describe these systems, necessitating development of models to understand their mechanisms. In this study, we image and quantitatively analyze the contractile kinematics observed in two ciliated protists (Vorticella sp. and Spirostomum sp.), and, based on the mechanochemistry of these organisms, we propose a minimal mathematical model that reproduces our observations as well as those published previously. Analyzing the model reveals three distinct dynamic regimes, differentiated by the rate of chemical driving and the importance of inertia. We characterize their unique scaling behaviors and kinematic signatures. Besides providing insights into Ca2+-powered myoneme contraction in protists, our work may also inform the rational design of ultrafast bioengineered systems such as active synthetic cells.}, number={25}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Floyd, Carlos and Molines, Arthur T. and Lei, Xiangting and Honts, Jerry E. and Chang, Fred and Elting, Mary Williard and Vaikuntanathan, Suriyanarayanan and Dinner, Aaron R. and Bhamla, M. Saad}, year={2023}, month={Jun} }
 @article{begley_elting_2023, title={Mitosis: Augmin-based bridges keep kinetochores in line}, volume={33}, ISSN={["1879-0445"]}, DOI={10.1016/j.cub.2022.12.037}, abstractNote={A recent study highlights the indispensability of the augmin complex for the construction of mitotic spindle bridging fibers, which in turn support accurate chromosome attachment and segregation.}, number={3}, journal={CURRENT BIOLOGY}, author={Begley, Marcus A. and Elting, Mary Williard}, year={2023}, month={Feb}, pages={R118–R121} }
 @article{moshtohry_bellingham-johnstun_elting_laplante_2022, title={Laser ablation reveals the impact of Cdc15p on the stiffness of the contractile ring}, volume={33}, ISSN={["1939-4586"]}, DOI={10.1091/mbc.E21-10-0515}, abstractNote={The mechanics that govern the constriction of the contractile ring remain poorly understood yet are critical to understanding the forces that drive cytokinesis. We used laser ablation in fission yeast cells to unravel these mechanics focusing on the role of Cdc15p as a putative anchoring protein. Our work shows that the severed constricting contractile ring recoils to a finite point leaving a gap that can heal if less than ∼1 µm. Severed contractile rings in Cdc15p-depleted cells exhibit an exaggerated recoil, which suggests that the recoil is limited by the anchoring of the ring to the plasma membrane. Based on a physical model of the severed contractile ring, we propose that Cdc15p impacts the stiffness of the contractile ring more than the viscous drag.}, number={6}, journal={MOLECULAR BIOLOGY OF THE CELL}, author={Moshtohry, Mohamed and Bellingham-Johnstun, Kimberly and Elting, Mary Williard and Laplante, Caroline}, year={2022}, month={May} }
 @article{zareiesfandabadi_elting_2022, title={p Force by minus-end motors Dhc1 and Klp2 collapses the S. pombe spindle after laser ablation}, volume={121}, ISSN={["1542-0086"]}, DOI={10.1016/j.bpj.2021.12.019}, abstractNote={A microtubule-based machine called the mitotic spindle segregates chromosomes when eukaryotic cells divide. In the fission yeast Schizosaccharomyces pombe, which undergoes closed mitosis, the spindle forms a single bundle of microtubules inside the nucleus. During elongation, the spindle extends via antiparallel microtubule sliding by molecular motors. These extensile forces from the spindle are thought to resist compressive forces from the nucleus. We probe the mechanism and maintenance of this force balance via laser ablation of spindles at various stages of mitosis. We find that spindle pole bodies collapse toward each other after ablation, but spindle geometry is often rescued, allowing spindles to resume elongation. Although this basic behavior has been previously observed, many questions remain about the phenomenon's dynamics, mechanics, and molecular requirements. In this work, we find that previously hypothesized viscoelastic relaxation of the nucleus cannot explain spindle shortening in response to laser ablation. Instead, spindle collapse requires microtubule dynamics and is powered by the minus-end-directed motor proteins dynein Dhc1 and kinesin-14 Klp2, but it does not require the minus-end-directed kinesin Pkl1.}, number={2}, journal={BIOPHYSICAL JOURNAL}, author={Zareiesfandabadi, Parsa and Elting, Mary Williard}, year={2022}, month={Jan}, pages={263–276} }
 @article{uzsoy_zareiesfandabadi_jennings_kemper_elting_2021, title={Automated tracking of S. pombe spindle elongation dynamics}, volume={6}, ISSN={["1365-2818"]}, url={https://doi.org/10.1111/jmi.13044}, DOI={10.1111/jmi.13044}, abstractNote={Abstract The mitotic spindle is a microtubule‐based machine that pulls the two identical sets of chromosomes to opposite ends of the cell during cell division. The fission yeast Schizosaccharomyces pombe is an important model organism for studying mitosis due to its simple, stereotyped spindle structure and well‐established genetic toolset. S. pombe spindle length is a useful metric for mitotic progression, but manually tracking spindle ends in each frame to measure spindle length over time is laborious and can limit experimental throughput. We have developed an ImageJ plugin that can automatically track S. pombe spindle length over time and replace manual or semi‐automated tracking of spindle elongation dynamics. Using an algorithm that detects the principal axis of the spindle and then finds its ends, we reliably track the length of the spindle as the cell divides. The plugin integrates with existing ImageJ features, exports its data for further analysis outside of ImageJ and does not require any programming by the user. Thus, the plugin provides an accessible tool for quantification of S. pombe spindle length that will allow automatic analysis of large microscopy data sets and facilitate screening for effects of cell biological perturbations on mitotic progression.}, journal={JOURNAL OF MICROSCOPY}, publisher={Wiley}, author={Uzsoy, Ana Sofia M. and Zareiesfandabadi, Parsa and Jennings, Jamie and Kemper, Alexander F. and Elting, Mary Williard}, year={2021}, month={Jul} }
 @article{elting_2021, title={Cytoskeletal biophysics: Passive crosslinker adapts to keep microtubule bundles on track}, volume={31}, ISSN={["1879-0445"]}, DOI={10.1016/j.cub.2021.04.065}, abstractNote={Assembly of the mitotic spindle requires dynamic adaptation and coordination among an array of motors and crosslinkers. A new study demonstrates in vitro how the mitotic crosslinker PRC1 can tune its behavior to regulate the speed of microtubule sliding.}, number={12}, journal={CURRENT BIOLOGY}, author={Elting, Mary Williard}, year={2021}, month={Jun}, pages={R793–R796} }
 @article{begley_solon_davis_sherrill_ohi_eltinga_2021, title={K-fiber bundles in the mitotic spindle are mechanically reinforced by Kif15}, volume={32}, ISSN={["1939-4586"]}, DOI={10.1091/mbc.E20-06-0426}, abstractNote={The mammalian kinetochore fiber (k-fiber) connects chromosomes to the spindle and supports segregation. We cut k-fibers by laser ablation to probe mechanical connections of microtubules within the bundle. We find that kinesin-12 Kif15 cross-links mediate k-fiber bundling. K-fiber bundling forces are in active competition with forces that cluster microtubule minus-ends.}, number={22}, journal={MOLECULAR BIOLOGY OF THE CELL}, author={Begley, Marcus A. and Solon, April L. and Davis, Elizabeth Mae and Sherrill, Michael Grant and Ohi, Ryoma and Eltinga, Mary Williard}, year={2021}, month={Dec} }
 @article{elting_suresh_dumont_2018, title={The Spindle: Integrating Architecture and Mechanics across Scales}, volume={28}, ISSN={0962-8924}, url={http://dx.doi.org/10.1016/J.TCB.2018.07.003}, DOI={10.1016/J.TCB.2018.07.003}, abstractNote={The spindle segregates chromosomes at cell division, and its task is a mechanical one. While we have a nearly complete list of spindle components, how their molecular-scale mechanics give rise to cellular-scale spindle architecture, mechanics, and function is not yet clear. Recent in vitro and in vivo measurements bring new levels of molecular and physical control and shed light on this question. Highlighting recent findings and open questions, we introduce the molecular force generators of the spindle, and discuss how they organize microtubules into diverse architectural modules and give rise to the emergent mechanics of the mammalian spindle. Throughout, we emphasize the breadth of space and time scales at play, and the feedback between spindle architecture, dynamics, and mechanics that drives robust function.}, number={11}, journal={Trends in Cell Biology}, publisher={Elsevier BV}, author={Elting, Mary Williard and Suresh, Pooja and Dumont, Sophie}, year={2018}, month={Nov}, pages={896–910} }
 @article{elting_prakash_udy_dumont_2017, title={Mapping Load-Bearing in the Mammalian Spindle Reveals Local Kinetochore Fiber Anchorage that Provides Mechanical Isolation and Redundancy}, volume={27}, ISSN={0960-9822}, url={http://dx.doi.org/10.1016/J.CUB.2017.06.018}, DOI={10.1016/J.CUB.2017.06.018}, abstractNote={Active forces generated at kinetochores move chromosomes, and the dynamic spindle must robustly anchor kinetochore fibers (k-fibers) to bear this load. The mammalian spindle bears the load of chromosome movement far from poles, but we do not know where and how—physically and molecularly—this load distributes across the spindle. In part, this is because probing spindle mechanics in live cells is difficult. Yet answering this question is key to understanding how the spindle generates and responds to force and performs its diverse mechanical functions. Here, we map load-bearing across the mammalian spindle in space-time and dissect local anchorage mechanics and mechanism. To do so, we laser-ablate single k-fibers at different spindle locations and in different molecular backgrounds and quantify the immediate relaxation of chromosomes, k-fibers, and microtubule speckles. We find that load redistribution is locally confined in all directions: along the first 3–4 μm from kinetochores, scaling with k-fiber length, and laterally within ∼2 μm of k-fiber sides, without detectable load sharing between neighboring k-fibers. A phenomenological model suggests that dense, transient crosslinks to the spindle along k-fibers bear the load of chromosome movement but that these connections do not limit the timescale of spindle reorganization. The microtubule crosslinker NuMA is needed for the local load-bearing observed, whereas Eg5 and PRC1 are not detectably required, suggesting specialization in mechanical function. Together, the data and model suggest that NuMA-mediated crosslinks locally bear load, providing mechanical isolation and redundancy while allowing spindle fluidity. These features are well suited to support robust chromosome segregation.}, number={14}, journal={Current Biology}, publisher={Elsevier BV}, author={Elting, Mary Williard and Prakash, Manu and Udy, Dylan B. and Dumont, Sophie}, year={2017}, month={Jul}, pages={2112–2122.e5} }
 @article{karg_elting_vicars_dumont_sullivan_2017, title={The chromokinesin Klp3a and microtubules facilitate acentric chromosome segregation}, volume={216}, ISSN={0021-9525 1540-8140}, url={http://dx.doi.org/10.1083/JCB.201604079}, DOI={10.1083/JCB.201604079}, abstractNote={Although poleward segregation of acentric chromosomes is well documented, the underlying mechanisms remain poorly understood. Here, we demonstrate that microtubules play a key role in poleward movement of acentric chromosome fragments generated in Drosophila melanogaster neuroblasts. Acentrics segregate with either telomeres leading or lagging in equal frequency and are preferentially associated with peripheral bundled microtubules. In addition, laser ablation studies demonstrate that segregating acentrics are mechanically associated with microtubules. Finally, we show that successful acentric segregation requires the chromokinesin Klp3a. Reduced Klp3a function results in disorganized interpolar microtubules and shortened spindles. Normally, acentric poleward segregation occurs at the periphery of the spindle in association with interpolar microtubules. In klp3a mutants, acentrics fail to localize and segregate along the peripheral interpolar microtubules and are abnormally positioned in the spindle interior. These studies demonstrate an unsuspected role for interpolar microtubules in driving acentric segregation.}, number={6}, journal={The Journal of Cell Biology}, publisher={Rockefeller University Press}, author={Karg, Travis and Elting, Mary Williard and Vicars, Hannah and Dumont, Sophie and Sullivan, William}, year={2017}, month={May}, pages={1597–1608} }
 @article{elting_udy_dumont_2016, title={Local Anchorage of Kinetochore-Fibers to the Mammalian Spindle Provides Mechanical Isolation and Load-Bearing Redundancy}, volume={110}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2015.11.1915}, DOI={10.1016/J.BPJ.2015.11.1915}, abstractNote={During cell division, kinetochores attach chromosomes to the spindle through microtubule bundles called k-fibers. Forces generated at kinetochores move chromosomes, rather than k-fibers; thus, the latter must be structurally anchored to the spindle. How a dynamic spindle robustly anchors its k-fibers is not understood. Here, we probe where and how the mammalian spindle holds on to its k-fibers to bear the load of chromosome movement. We use laser ablation to sever k-fibers at different locations and detach them from spindle poles, thereby revealing their anchorage within the spindle body. The immediate relaxation response post-ablation indicates that k-fibers are anchored not only at their ends, but also along their lengths within the spindle. Effective anchorage scales with k-fiber length for the first few microns, but then saturates, indicating that k-fibers are effectively locally anchored within the first few microns of their lengths. This anchorage also occurs locally along the spindle's width, as little load is shared between neighboring k-fibers. We find that increasing microtubule crosslinking increases k-fiber anchorage, and that depleting NuMA, known to crosslink microtubules at poles, significantly disrupts local anchorage of k-fibers to the spindle body. In contrast, depletion of microtubule crosslinkers Eg5 and PRC1 does not affect anchorage despite these proteins’ local mechanical functions. Together, the data indicate that NuMA-mediated microtubule crosslinking in the spindle body allows for local anchorage and isolation of k-fibers, and mechanical redundancy in their connections to the spindle. Such mechanical isolation and redundancy are well-suited to ensure robust k-fiber load-bearing and chromosome segregation despite dynamic spindle forces and structures.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Elting, Mary W. and Udy, Dylan B. and Dumont, Sophie}, year={2016}, month={Feb}, pages={355a} }
 @article{elting_hueschen_udy_dumont_2014, title={Force on spindle microtubule minus ends moves chromosomes}, volume={206}, ISSN={1540-8140 0021-9525}, url={http://dx.doi.org/10.1083/JCB.201401091}, DOI={10.1083/JCB.201401091}, abstractNote={The spindle is a dynamic self-assembling machine that coordinates mitosis. The spindle’s function depends on its ability to organize microtubules into poles and maintain pole structure despite mechanical challenges and component turnover. Although we know that dynein and NuMA mediate pole formation, our understanding of the forces dynamically maintaining poles is limited: we do not know where and how quickly they act or their strength and structural impact. Using laser ablation to cut spindle microtubules, we identify a force that rapidly and robustly pulls severed microtubules and chromosomes poleward, overpowering opposing forces and repairing spindle architecture. Molecular imaging and biophysical analysis suggest that transport is powered by dynein pulling on minus ends of severed microtubules. NuMA and dynein/dynactin are specifically enriched at new minus ends within seconds, reanchoring minus ends to the spindle and delivering them to poles. This force on minus ends represents a newly uncovered chromosome transport mechanism that is independent of plus end forces at kinetochores and is well suited to robustly maintain spindle mechanical integrity.}, number={2}, journal={The Journal of Cell Biology}, publisher={Rockefeller University Press}, author={Elting, Mary Williard and Hueschen, Christina L. and Udy, Dylan B. and Dumont, Sophie}, year={2014}, month={Jul}, pages={245–256} }
 @article{elting_hueschen_udy_dumont_2014, title={Probing Forces on Newly Generated Spindle Microtubule Minus-Ends}, volume={106}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2013.11.100}, DOI={10.1016/J.BPJ.2013.11.100}, number={2}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Elting, Mary W. and Hueschen, Christina L. and Udy, Dylan B. and Dumont, Sophie}, year={2014}, month={Jan}, pages={9a–10a} }
 @article{hueschen_elting_udy_dumont_2014, title={Probing Forces on Newly Generated Spindle Microtubule Minus-Ends}, volume={106}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/J.BPJ.2013.11.4314}, DOI={10.1016/J.BPJ.2013.11.4314}, abstractNote={The mitotic spindle is a dynamic self-organizing machine that coordinates cell division and preserves genomic stability. The ability to focus microtubule minus-ends into poles is crucial to spindle structure and function. However, our understanding of pole-focusing forces has been limited by the challenges of labeling and imaging microtubule minus-ends in established spindles. Here, we used laser ablation to sever kinetochore-fiber microtubules in mammalian cells and probe how the cell detects and organizes newly generated microtubule minus-ends. Within a few seconds of ablation, the cell recognizes new minus-ends and begins pulling them poleward. These pole-focusing forces exist throughout metaphase and anaphase and can move chromosomes rapidly, dominating other spindle forces. Opposing forces on chromosomes from the other half-spindle are able to slow, though not stop, the pole-focusing response, as indicated by faster pole-focusing speeds in monopolar spindles and during anaphase than in metaphase bipolar spindles. Together, our data indicate that microtubule minus-end focusing forces operate broadly and rapidly and are of similar magnitude to other spindle forces. These pole-focusing forces are thus well-suited to robustly maintain spindle structural integrity despite rapid turnover of spindle components and mechanical challenges.}, number={2}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Hueschen, Christina L. and Elting, Mary W. and Udy, Dylan B. and Dumont, Sophie}, year={2014}, month={Jan}, pages={787a} }
 @article{elting_spudich_2012, title={Future Challenges in Single-Molecule Fluorescence and Laser Trap Approaches to Studies of Molecular Motors}, volume={23}, ISSN={1534-5807}, url={http://dx.doi.org/10.1016/j.devcel.2012.10.002}, DOI={10.1016/j.devcel.2012.10.002}, abstractNote={Single-molecule analysis is a powerful modern form of biochemistry, in which individual kinetic steps of a catalytic cycle of an enzyme can be explored in exquisite detail. Both single-molecule fluorescence and single-molecule force techniques have been widely used to characterize a number of protein systems. We focus here on molecular motors as a paradigm. We describe two areas where we expect to see exciting developments in the near future: first, characterizing the coupling of force production to chemical and mechanical changes in motors, and second, understanding how multiple motors work together in the environment of the cell.}, number={6}, journal={Developmental Cell}, publisher={Elsevier BV}, author={Elting, Mary Williard and Spudich, James A.}, year={2012}, month={Dec}, pages={1084–1091} }
 @article{sung_choe_elting_nag_sutton_deacon_leinwand_ruppel_spudich_2012, title={Single Molecule Studies of Recombinant Human α- and β-Cardiac Myosin to Elucidate Molecular Mechanism of Familial Hypertrophic and Dilated Cardiomyopathies}, volume={102}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2011.11.3345}, DOI={10.1016/j.bpj.2011.11.3345}, abstractNote={Hypertrophic cardiomyopathies (HCM) and dilated cardiomyopathies (DCM) are common inherited cardiovascular diseases, often resulting from single point mutations in genes encoding sarcomeric proteins. Genetic and clinical studies have identified several hundred mutations, including severe disease causing mutations in β-myosin heavy chain (MHC). Despite the clinical significance, few single molecule studies exist for mutated β-cardiac myosin, primarily due to difficulties of heterologous protein expression and instrumental limitations. Previous studies have used mouse α-cardiac myosin or biopsies from patients. Those studies are not optimal to understand the molecular mechanism of HCM/DCM because there are significant differences between mouse α- and human β-MHC. Furthermore, biopsy samples from patients are often inhomogeneous mixtures of wildtype (wt) and mutants. This may explain why there have been many inconsistencies between the previous studies. Here, we demonstrate the first single molecule studies of recombinant human cardiac myosin. We expressed homogenous and fully functional wt human cardiac α- and β-S1 with human light chains bound. Then, we characterized the actin-myosin interaction using in vitro motility and laser beam trapping assays. From the in vitro motility assay, we measured the maximum velocity from wt α- and β-S1. Using the laser trap, we measured stroke sizes, ATP binding rates (low [ATP]) and ADP release rates (high [ATP]). Furthermore, we expressed several HCM (R403Q, S453C) and DCM (S532P) causing mutants, and obtained preliminary in vitro motility and trap data. We have built a modern version optical trap that can resolve the ∼10 nm stroke size and ∼10 ms strongly bound state of cardiac β-S1 at high [ATP]. We have further improved the resolution by implementing real-time feedback control in the system to accurately determine fine changes caused by the single mutations.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Sung, Jongmin and Choe, Elizabeth and Elting, Mary and Nag, Suman and Sutton, Shirley and Deacon, John and Leinwand, Leslie and Ruppel, Kathy and Spudich, James}, year={2012}, month={Jan}, pages={613a–614a} }
 @article{elting_bryant_liao_spudich_2011, title={Detailed Tuning of Structure and Intramolecular Communication Are Dispensable for Processive Motion of Myosin VI}, volume={100}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2010.11.045}, DOI={10.1016/j.bpj.2010.11.045}, abstractNote={Dimeric myosin VI moves processively hand-over-hand along actin filaments. We have characterized the mechanism of this processive motion by measuring the impact of structural and chemical perturbations on single-molecule processivity. Processivity is maintained despite major alterations in lever arm structure, including replacement of light chain binding regions and elimination of the medial tail. We present kinetic models that can explain the ATP concentration-dependent processivities of myosin VI constructs containing either native or artificial lever arms. We conclude that detailed tuning of structure and intramolecular communication are dispensable for processive motion, and further show theoretically that one proposed type of nucleotide gating can be detrimental rather than beneficial for myosin processivity.}, number={2}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Elting, Mary Williard and Bryant, Zev and Liao, Jung-Chi and Spudich, James A.}, year={2011}, month={Jan}, pages={430–439} }
 @article{elting_bryant_liao_spudich_2010, title={Probing Myosin-VI Processivity using Artificial Lever Arms}, volume={98}, ISSN={0006-3495}, url={http://dx.doi.org/10.1016/j.bpj.2009.12.3962}, DOI={10.1016/j.bpj.2009.12.3962}, abstractNote={The lever arm of myosin VI has an unusual composition in which two different calmodulin-binding domains, a globular three-helix bundle, and an extended single alpha-helix domain may all contribute structural roles. We wish to understand which properties of this lever arm are important for mediating intra-head communication, preventing dissociation from the actin filament, and determining the distribution of stride sizes in a processively stepping dimer. We have replaced parts of the myosin VI lever arm with alpha-actinin repeats in a series of chimeric constructs. In dimers with artifical levers arms, we have found that processivity is surprisingly robust to dramatic changes in the properties of the lever arm, even when the stride size is altered (Liao et al., JMB 2009). In new chimeric constructs, we show that limited processivity is possible even in the absence of both calmodulin-binding regions. We examine the importance of intra-head coordination for processive motion in myosin VI by comparing the predictions of simple kinetic models to measurements of run length distributions for chimeric myosins and for control contructs.}, number={3}, journal={Biophysical Journal}, publisher={Elsevier BV}, author={Elting, Mary W. and Bryant, Zev D. and Liao, Jung-Chi and Spudich, James A.}, year={2010}, month={Jan}, pages={723a} }
 @article{liao_elting_delp_spudich_bryant_2009, title={Engineered Myosin VI Motors Reveal Minimal Structural Determinants of Directionality and Processivity}, volume={392}, ISSN={0022-2836}, url={http://dx.doi.org/10.1016/j.jmb.2009.07.046}, DOI={10.1016/j.jmb.2009.07.046}, abstractNote={Myosins have diverse mechanical properties reflecting a range of cellular roles. A major challenge is to understand the structural basis for generating novel functions from a common motor core. Myosin VI (M6) is specialized for processive motion toward the (−) end of actin filaments. We have used engineered M6 motors to test and refine the “redirected power stroke” model for (−) end directionality and to explore poorly understood structural requirements for processive stepping. Guided by crystal structures and molecular modeling, we fused artificial lever arms to the catalytic head of M6 at several positions, retaining varying amounts of native structure. We found that an 18-residue α-helical insert is sufficient to reverse the directionality of the motor, with no requirement for any calmodulin light chains. Further, we observed robust processive stepping of motors with artificial lever arms, demonstrating that processivity can arise without optimizing lever arm composition or mechanics.}, number={4}, journal={Journal of Molecular Biology}, publisher={Elsevier BV}, author={Liao, Jung-Chi and Elting, Mary Williard and Delp, Scott L. and Spudich, James A. and Bryant, Zev}, year={2009}, month={Oct}, pages={862–867} }