Abstract
To examine the relationship between the growth polarity of microtubules and guanine nucleotide dependence, we polymerized microtubules from axonemes either with GTP or with GTP and GDP, and observed individual microtubules by dark-field microscopy. We used a perfusion chamber to monitor the growth polarity of microtubules from the same axoneme. Exchanging a solution containing only GTP for one containing GTP and GDP elicited a switch in the growth polarity of microtubules from the plus ends to the minus ends. These results suggest that GDP directly affects microtubule polymerization and inverts growth polarity, probably by inhibiting growth at the plus ends.
