The cofactor-dependent pathways for alpha- and beta-tubulins in microtubule biogenesis are functionally different in fission yeast.
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 alpha-/beta-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 beta-tubulin, but not in alpha-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.
Radcliffe
P A
PA
Laboratory of Cell Regulation, Imperial Cancer Research Fund, London WC2A 3PX, United Kingdom.
Garcia
M A
MA
Toda
T
T
D000595:Amino Acid Sequence; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005800:Genes, Fungal; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism*; D008969:Molecular Sequence Data; D012568:Schizosaccharomyces / Q000235:genetics* / Q000378:metabolism* / Q000648:ultrastructure; D029702:Schizosaccharomyces pombe Proteins; D017386:Sequence Homology, Amino Acid; D014404:Tubulin / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics
C110653:Alp1 protein, S pombe; D005656:Fungal Proteins; D008869:Microtubule-Associated Proteins; D029702:Schizosaccharomyces pombe Proteins; D014404:Tubulin