Microtubular dynamics of Saccharomyces cerevisiae temperature-sensitive secretory mutants: the sec 1 product and polymerization of microtubules.

The relation of cytoplasmic microtubules to intracellular transport was studied in temperature-sensitive (ts) secretory mutants of Saccharomyces cerevisiae at permissive and nonpermissive temperature using indirect immunofluorescence with monoclonal antibody TU-01 against alpha-tubulin. It was found that in the sec 1 mutant, which at 37 degrees C accumulated secretory vesicles and in which therefore transport of secretory material from secretory vesicles to cytoplasmic membrane was inhibited, cytoplasmic and in some cases nuclear microtubules were impaired. After 4 h of postcultivation at 24 degrees C the altered phenotype reverted to the original state, the cells began to divide, and were comparable with control. Use of the sec 1 mutant protoplasts suggested that the product, whose gene is mutated, is probably involved in microtubular polymerization. The sec 7 mutant, which accumulates the Golgi complex under nonpermissive conditions and in which the transfer of secretory material from the Golgi complex to the secretory vesicles is thus inhibited, showed no significant changes in the length or number of cytoplasmic microtubules. As a result of secretory product accumulation, the cytoplasmic microtubules were displaced towards the periphery in some cells.