On the role of the tubulin nonexchangeable GTP site in bovine neurotubule assembly.

A procedure for radiolabeling the terminal phosphoryl group of the tubulin nonexchangeable GTP site using bacterial acetate kinase and acetyl-32P is described. Warming such samples to 37 degrees results in microtubule assembly and hydrolysis of the nonexchangeable site GTP in a parallel fashion. Removal of the microtubule-associated protein fraction from lebeled tubulin prevents hydrolysis and assembly, and recombination of these components restores both processes again in a parallel fashion. These and other experiments indicate that the nonexchangeable site GTP hydrolysis and assembly are intimately linked. The experiments also demonstrate that GRP is not required at the exchangeable nucleotide site for assembly to occur.