Oligomeric tubulin in large transporting complex is transported via kinesin in squid giant axone

Slow axonal transport depends on an active mechanism that conveys cytosolic proteins. To investigate its molecular mechanism, we now constructed an in vitro experimental system for observation of tubulin transport, using squi d giant axons. After injecting fluorescence-labeled tubulin into the axons, we monitored the movement of fluorescence by confocal laser scanning micro scopy and fluorescence correlation spectroscopy. Here, from the pharmacolog ical experiments and the functional blocking of kinesin motor protein by an ti-kinesin antibody, we show that the directional movement of fluorescent p rofile was dependent on kinesin motor function. The fluorescent correlation function and estimated translational diffusion time revealed that tubulin molecule was transported in a unique form of large transporting complex dis tinct from those of stable polymers or other cytosolic protein.