The Cofactor-Dependent Pathways for - and ß-Tubulins in Microtubule Biogenesis Are Functionally Different in Fission Yeast

Corresponding author: Takashi Toda, Laboratory of Cell Regulation, Imperial Cancer Research Fund, P.O. Box 123, 44 Lincoln's Inn Fields, London WC2A 3PX, United Kingdom., toda{at}europa.lif.icnet.uk (E-mail)

Communicating editor: P. RUSSELL

The biogenesis of microtubules in the cell comprises a series of complex steps, including protein-folding reactions catalyzed by chaperonins. In addition a group of evolutionarily conserved proteins, called cofactors (A to E), is required for the production of assembly-competent -/ß-tubulin heterodimers. Using fission yeast, in which alp11⁺, alp1⁺, and alp21⁺, encoding the homologs for cofactors B, D, and E, respectively, are essential for cell viability, we have undertaken the genetic analysis of alp31⁺, the homolog of cofactor A. Gene disruption analysis shows that, unlike the three genes mentioned above, alp31⁺ is dispensable for cell growth and division. Nonetheless, detailed analysis of alp31-deleted cells demonstrates that Alp31^A is required for the maintenance of microtubule structures and, consequently, the proper control of growth polarity. alp31-deleted cells show genetic interactions with mutations in ß-tubulin, but not in -tubulin. Budding yeast cofactor A homolog RBL2 is capable of suppressing the polarity defects of alp31-deleted cells. We conclude that the cofactor-dependent biogenesis of microtubules comprises an essential and a nonessential pathway, both of which are required for microtubule integrity.

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