THE MICROTUBULE LATTICE - 20 YEARS ON

In 1974, optical diffraction and image analysis indicated that tubulin dimers in the cylindrically complete A-tubule of flagellar doublet mi crotubules are arranged with helical symmetry, while those in the inco mplete B-tubule associate differently. Recently, electron micrographs of reassembled brain microtubules decorated with kinesin heads have sh own that the tubulin dimers there are arranged as in the B-tubule. The lack of symmetry of microtubules assembled in vitro prompts Linda Amo s to speculate here that the assembly process in vitro may differ from that occurring in the cell.