α-tubulin regulation by 5' introns in Saccharomyces cerevisiae.

Across eukaryotic genomes, multiple α- and ß-tubulin genes require regulation to ensure sufficient production of tubulin heterodimers. Features within these gene families that regulate expression remain underexplored. Here, we investigate the role of the 5' intron in regulating α-tubulin expression in Saccharomyces cerevisiae. We find that the intron in the α-tubulin, TUB1, promotes α-tubulin expression and cell fitness during microtubule stress. The role of the TUB1 intron depends on proximity to the TUB1 promoter and sequence features that are distinct from the intron in the alternative α-tubulin isotype, TUB3. These results lead us to perform a screen to identify genes that act with the TUB1 intron. We identified several genes involved in chromatin remodeling, α/ß-tubulin heterodimer assembly, and the spindle assembly checkpoint. We propose a model where the TUB1 intron promotes expression from the chromosomal locus and that this may represent a conserved mechanism for tubulin regulation under conditions that require high levels of tubulin production.

Tubulin isotype regulation maintains asymmetric requirement for α-tubulin over ß-tubulin.

How cells regulate α- and ß-tubulin to meet the demand for αß-heterodimers and avoid consequences of monomer imbalance is not understood. We investigate the role of gene copy number and how shifting expression of α- or ß-tubulin genes impacts tubulin proteostasis and microtubule function in Saccharomyces cerevisiae. We find that α-tubulin gene copy number is important for maintaining excess α-tubulin protein compared to ß-tubulin protein. Excess α-tubulin prevents accumulation of super-stoichiometric ß-tubulin, which leads to loss of microtubules, formation of non-microtubule assemblies of tubulin, and disrupts cell proliferation. In contrast, sub-stoichiometric ß-tubulin or overexpression of α-tubulin has minor effects. We provide evidence that yeast cells equilibrate α-tubulin protein concentration when α-tubulin isotype expression is increased. We propose an asymmetric relationship between α- and ß-tubulins, in which α-tubulins are maintained in excess to supply αß-heterodimers and limit the accumulation of ß-tubulin monomers.

Microtubule cytoskeleton: Revealing new readers of the tubulin code.

Microtubule networks are thought to be controlled by an elaborate program of tubulin posttranslational modifications and proteins that selectively bind to modified states. A new study identifies proteins that bind tyrosinated tubulin, revealing a novel recognition mechanism.