Sliding of stable tubule only polypeptide proteins on microtubules

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Abstract
Microtubules [bovine brain] are stabilized against cold temperature disassembly by 145-kilodalton proteins [stable tubule only polypeptides (STOP)] that block the end-wise dissociation of subunits from the polymers. Several kinetic parameters of the interaction of STOP with microtubules are described here. STOP will bind to microtubules either during assembly of the polymer or at steady state. The addition appears random on the polymers and does not require the mediation of tubulin subunits. Tubulin subunits compete with microtubules for STOP binding, but binding to the polymers is apparently irreversible. STOP do not exchange measurably between polymers at steady-state. Nonetheless, a displacement of STOP within a single polymer is readily demonstrable. The displacement is apparently due to a surface translocation, or sliding, of STOP on microtubules.