Determination of the Net Exchange Rate of Tubulin Dimer in Steady-State Microtubules by Fluorescence Correlation Spectroscopy

The microtubule cytoskeleton plays an important role in eukaryotic cells, e. g., in cell movement or morphogenesis. Microtubules, formed by assembly of tubulin dimers, are dynamic polymers changing randomly between periods of growing and shortening, a property known as dynamic instability. Another process characterizing the dynamic behaviour is the socalled treadmilling due to different binding constants of tubulin at both microtubule ends. In this study, we used tetramethylrhodamine (TMR)labeled tubulin added to microtubule suspensions to determine the net exchange rate (NER) of tubulin dimers by fluorescence correlation spectroscopy (FCS) as a measure for microtubule dynamics. This approach, which seems to be suitable as screening system to detect compounds influencing the NER of tubulin dimers into microtubules at steadystate, showed that taxol, nocodazole, colchicine, and vinblastine affect microtubule dynamics at concentrations as low as 10[-9] 10[-10] M.