Distribution of gamma-tubulin in higher plant cells: Cytosolic gamma-tubulin is part of high molecular weight complexes

gamma-Tubulin is a protein found in ail eukaryotic cells, where it plays a key role in the nucleation of microtubules. in higher plant cells, gamma-tu bulin is localized at the nuclear surface, a known microtubule-organizing c entre, and is codistributed with all microtubule arrays. Functions of plant gamma-tubulin remain to be determined. This study describes some propertie s of higher plant y-tubulin. The overall level of gamma-tubulin was constan t during the cell cycle in synchronized tobacco BY-2 cells. Biochemical ana lysis of the subcellular distribution of gamma-tubulin in maize cells revea led that, in contrast with animal gamma-tubulin, plant gamma-tubulin is mai nly associated with endomembranes. We showed for the first time that the po ol of soluble cytosolic gamma-tubuin contained two main gamma-tubulin compl exes. gamma-tubulin, Hsp70 and TCP1-related proteins might interact in a sm all complex of 750 kDa. A second gamma-tubulin complex, larger than 1500 kD a was purified. The protein profile of this large complex was very similar to animal gamma-tubulin complexes. The putative functions of these two comp lexes in plant microtubule nucleation are discussed.