A mutation in gamma-tubulin alters microtubule dynamics and organization and is synthetically lethal with the kinesin-like protein Pkl1p

Mitotic segregation of chromosomes requires spindle pole functions for micr otubule nucleation, minus end organization, and regulation of dynamics. gam ma-Tubulin is essential for nucleation, and we now extend its role to these latter processes. We have characterized a mutation in gamma-tubulin that r esults in cold-sensitive mitotic arrest with an elongated bipolar spindle b ut impaired anaphase A. At 30 degrees C cytoplasmic microtubule arrays are abnormal and bundle into single larger arrays. Three-dimensional time-lapse video microscopy reveals that microtubule dynamics are altered. Localizati on of the mutant gamma-tubulin is like the wild-type protein. Prediction of gamma-tubulin structure indicates that non-alpha/beta-tubulin protein-prot ein interactions could be affected. The kinesin-like protein (klp) Pkl1p lo calizes to the spindle poles and spindle and is essential for viability of the gamma-tubulin mutant and in multicopy for normal cell morphology at 30 degrees C. Localization and function of Pkl1p in the mutant appear unaltere d, consistent with a redundant function for this protein in wild type. Our data indicate a broader role for gamma-tubulin at spindle poles in regulati ng aspects of microtubule dynamics and organization. We propose that Pkl1p rescues an impaired function of gamma-tubulin that involves non-tubulin pro tein-protein interactions, presumably with a second motor, MAP, or MTOC com ponent.