. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 218 REPORTS FROM THE MBL GENERAL SCIENTIFIC MEETINGS Reference: Biol. Bull 193: 2IS-2I9. (October. 1997) UV Cutting of MAPs-bound Microtubules Phong T. Tran], E. D. Salmon*, and Shinyu Inoue (Marine Biological Laboraton. Woods Hole, Massachusetts 02543) Microtubules exhibit dynamic instability in vivo and in vitro (with purified tubulin). stochastically switching between phases of persistent growth and shortening (reviewed in ref. 1). The growth phase is governed by the presence of a tubulin GTP cap at the end of the microtu
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 218 REPORTS FROM THE MBL GENERAL SCIENTIFIC MEETINGS Reference: Biol. Bull 193: 2IS-2I9. (October. 1997) UV Cutting of MAPs-bound Microtubules Phong T. Tran], E. D. Salmon*, and Shinyu Inoue (Marine Biological Laboraton. Woods Hole, Massachusetts 02543) Microtubules exhibit dynamic instability in vivo and in vitro (with purified tubulin). stochastically switching between phases of persistent growth and shortening (reviewed in ref. 1). The growth phase is governed by the presence of a tubulin GTP cap at the end of the microtubule. and the structure we observe is tubulin protofilament sheet folded up into a blunt and straight microtubule. The shortening phase is initiated by the loss of the tubulin GTP cap, and we see the blossom structure of protofil- aments, curved inside-out. The transitions back and forth be- tween the growth and shortening phases include an intermediate phase in which the microtubule has lost its tubulin GTP cap but still, transiently, retains the straight, blunt structure chracter- istic of the growth phase (2). Thus, for a microtubule to grow, new subunits must be added to the tubulin GTP cap; loss of the cap puts the microtubule in the intermediate phase. And for a microtubule to shorten, the protofilaments must first peel away from the central lattice and subsequently break off (3). If micro- tubules are polymerized with purified tubulin. cutting off the tubulin GTP cap, either mechanically or with UV, produces microtubules in the intermediate phase (2). For plus ends, the intermediate phase quickly switches to the shortening phase. For minus ends, the intermediate phase quickly switches back to the growth phase (2). Microtubule-associated-proteins (MAPs)—particularly neuronal MAPs such as MAP2 or Tau — have been shown to suppress microtubule dynamics (4). To test the hypothesis that MAPs promote switching from the interme- diate to the growth phase, we used UV irradiat
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