The carboxy terminus of Tub4p is required for gamma-tubulin function in budding yeast

The role of gamma -tubulin in microtubule nucleation is well established, h owever, its function in other aspects of microtubule organization is unknow n. The carboxy termini of alpha/beta -tubulins influence the assembly and s tability of microtubules. We investigated the role of the carboxy terminus of yeast gamma -tubulin (Tub4p) in microtubule organization. This region co nsists of a conserved domain (DSYLD), and acidic tail, Cells expressing tru ncations lacking the DSYLD domain, tail or both regions are temperature sen sitive for growth. Growth defects of tub4 mutants lacking either or both ca rboxy-terminal domains are suppressed by the microtubule destabilizing drug benomyl. tub4 carboxy-terminal mutants arrest as large budded cells with s hort bipolar spindles positioned at the bud neck. Electron microscopic anal ysis of wild-type and CTR mutant cells reveals that SPBs are tightly associ ated with the bud neck/cortex by cytoplasmic microtubules in mutants lackin g the tail region (tub4-Delta 444, tub4-Delta 448). Mutants lacking the DSY LD residues (tub4-Delta 444, tub4-Delta DSYLD) form many cytoplasmic microt ubules, We propose that the carboxy terminus of Tub4p is required for re-or ganization of the microtubules upon completion of nuclear migration, and fa cilitates spindle elongation into the bud.