A Novel Step in β-Tubulin Folding Is Important for Heterodimer Formation in Saccharomyces cerevisiae

Abstract

Undimerized β-tubulin is toxic in the yeast S. cerevisiae. It can arise if levels of β-tubulin and α-tubulin are unbalanced or if the tubulin heterodimer dissociates. We are using the toxicity of β-tubulin to understand early steps in microtubule morphogenesis. We find that deletion of PLP1 suppresses toxic β-tubulin formed by disparate levels of α- and β-tubulin. That suppression occurs either when α-tubulin is modestly underexpressed relative to β-tubulin or when β-tubulin is inducibly and strongly overexpressed Plp]1p does not affect tubulin expression. Instead, a significant proportion of the undimerized β-tubulin in plp1Δ cells is less toxic than that in wild-type cells. It is also less able to combine with α-tubulin to form a heterodimer. As a result, plp1Δ cells have lower levels of heterodimer. Importantly, plp1Δ cells that also lack Pac10, a component of the GimC/PFD complex, are even less affected by free β-tubulin. Our results suggest that Plp1p defines a novel early step in β-tubulin folding.