Distribution of γ‐Tubulin in Higher Plant Cells: Cytosolic γ‐Tubulin is Part of High Molecular Weight Complexes

Abstract

Abstract: γ‐Tubulin is a protein found in all eukaryotic cells, where it plays a key role in the nucleation of microtubules. In higher plant cells, γ‐tubulin is localized at the nuclear surface, a known microtubule‐organizing centre, and is codistributed with all microtubule arrays. Functions of plant γ‐tubulin remain to be determined. This study describes some properties of higher plant γ‐tubulin. The overall level of γ‐tubulin was constant during the cell cycle in synchronized tobacco BY‐2 cells. Biochemical analysis of the subcellular distribution of γ‐tubulin in maize cells revealed that, in contrast with animal γ‐tubulin, plant γ‐tubulin is mainly associated with endomembranes. We showed for the first time that the pool of soluble cytosolic γ‐tubulin contained two main γ‐tubulin complexes. γ‐tubulin, Hsp70 and TCP1‐related proteins might interact in a small complex of 750 kDa. A second γ‐tubulin complex, larger than 1500 kDa was purified. The protein profile of this large complex was very similar to animal γ‐tubulin complexes. The putative functions of these two complexes in plant microtubule nucleation are discussed.