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Mol Cell Biol, March 1998, p. 1757-1762, Vol. 18, No. 3
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Formation and Function of the Rbl2p--Tubulin Complex

Julie E. Archer, Margaret Magendantz, Leticia R. Vega, and Frank Solomon^*

Department of Biology and Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Received 3 July 1997/Returned for modification 22 August 1997/Accepted 22 December 1997

The yeast protein Rbl2p suppresses the deleterious effects of excess -tubulin as efficiently as does -tubulin. Both in vivo and in vitro, Rbl2p forms a complex with -tubulin that does not contain -tubulin, thus defining a second pool of -tubulin in the cell. Formation of the complex depends upon the conformation of -tubulin. Newly synthesized -tubulin can bind to Rbl2p before it binds to -tubulin. Rbl2p can also bind -tubulin from the /-tubulin heterodimer, apparently by competing with -tubulin. The Rbl2p--tubulin complex has a half-life of ~2.5 h and is less stable than the /-tubulin heterodimer. The results of our experiments explain both how excess Rbl2p can rescue cells overexpressing -tubulin and how it can be deleterious in a wild-type background. They also suggest that the Rbl2p--tubulin complex is part of a cellular mechanism for regulating the levels and dimerization of tubulin chains.

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^* Corresponding author. Mailing address: Department of Biology and Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139. Phone: (617) 253-3026. Fax: (617) 253-6272. E-mail: solomon{at}mit.edu.

Present address: Department of Biological Sciences, California Institute of Technology, Pasadena, Calif.

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