J. Biol. Chem., Vol. 265, Issue 3, 1414-1418, Jan, 1990
Mechanism for oscillatory assembly of microtubules
M Caplow and J Shanks
Department of Biochemistry, University of North Carolina, Chapel Hill 27599-7260.
Dampened oscillations of microtubule assembly can accompany polymerization
at high tubulin subunit concentrations. This presumably results from a
synchronization of dynamic instability behavior, which generates a large
population of rapidly disassembling microtubules, that liberate tubulin-GDP
oligomers. Subunits in oligomers cannot assemble until they dissociate, to
allow GDP-GTP exchange. To determine whether rapidly disassembling
microtubules generate oligomers directly, we measured the rate of
dilution-induced disassembly of tubulin-GDP microtubules and the rate of
dissociation of GDP from the so-formed tubulin-GDP subunits. The rate of
GDP dissociation from liberated subunits was found to correspond to that of
tubulin-GDP subunits (t1/2 = 5 s), rather than tubulin-GDP oligomers. This
indicates that tubulin- GDP subunits are released from microtubules
undergoing rapid disassembly. Oligomers apparently form in a side reaction
from the high concentration of tubulin-GDP subunits liberated from the
synchronously disassembling microtubule population. The rate of subunit
dissociation is 0.11 s-1 with oligomers formed by concentrating tubulin-GDP
subunits and 0.045 s-1 with oligomers formed by cold-induced microtubule
disassembly. This difference provides evidence that the conformation of
tubulin-GDP subunits released from rapidly disassembling microtubules
differs from tubulin-GDP subunits that were not recently in the microtubule
lattice.
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