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![[Figure 5]](id5005fig5mag.jpg)
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Figure 5
Dynamic MT end structure visualized in vitro by cryo-electron tomography. (a) Longitudinal slice through the tomographic reconstruction, showing a range of MT end morphologies including the highly characteristic `rams horn'-like appearance associated with depolymerizing MTs (pink arrows) and the relatively short flared region associated with growing MTs (red arrowhead). (b) Top, longitudinal slice through the tomographic reconstruction, showing a dynamic MT (of unknown polarity) in which one end is visible. Bottom, a series of transverse sections through the tomographic reconstruction, showing the transition from lattice to end. As was seen in GMPCPP MTs (Fig. 2 ![[link]](../../../../../../logos/arrows/d_arr.gif) a), the cylindrical organization of the MT is retained even as PFs are lost, until a critical point when the PFs curve gently away from the MT axis in a sheet, often remaining laterally connected until the very end of the MT. (c) Three-dimensional surface rendering of plus (purple, left) and minus (yellow, middle) depolymerizing MT ends compared with a model MT end as described for Fig. 2(b). A range of tubulin curvature is observed in minus and plus ends, with peeling PFs exhibiting a similar curvature to curved tubulin PDB structures. (d) Centre, longitudinal section through a tomogram of two MTs each with a small lattice defect indicated by blue arrows. Insets, transverse sections through these MTs with positions of sections relative to the MT and their rotational average indicated in colour. (e) Left, longitudinal section through a tomogram of an MT, with a blue arrow indicating a small lattice defect. Insets, transverse sections through the same MT with the position of sections relative to the polymer and their rotational average indicated in colour, showing the change in PF number that coincides with the defect. (f) Left, longitudinal section through a tomogram of a 13PF MT, with a blue arrow indicating a small lattice defect that coincides with a change in helical symmetry. Insets; centre, Fourier filtered two-dimensional projection of this MT, showing a change in characteristic moiré pattern from a 13PF with a 3-start (top section) to a 13PF with a 2-start (bottom section); right, transverse sections through the same MT with the position of the section relative to the polymer and their rotational average indicated in colour. (g) Left, Fourier filtered two-dimensional projection image of three MTs: a 14PF (left), a 13PF (right) and an incomplete tube (centre, red `o' for `open'). Centre, longitudinal slice through a three-dimensional tomogram of the three MTs. Right; transverse slice, at the position indicated with a light blue dashed line, through the three-dimensional tomogram of the three MTs. Note the less complex moiré pattern of the incomplete tube because only a single polymer surface is projected in the image. |
![[Figure 5]](id5005fig5.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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