Amino acid-level differences in alpha tubulin sequences are uniquely required for meiosis

Tubulin is the major structural constituent of the microtubule cytoskeleton. Yeast Schizosaccharomyces pombe contain two α- tubulins genes, nda2 and atb2, that are highly functionally distinct: nda2 deletion is lethal, while lack of atb2 does not interfere with cell viability. The functional determinants underlying this distinction are unknown. Here we used CRISPR-Cas9 gene editing to generate a yeast strain expressing Atb2 amino acid sequence utilizing Nda2 codon usage in the native Nda2 locus. Such Nda2-coded Atb2 (NCA) yeast, unlike Nda2 knockout, were viable and displayed no visible abnormalities in cell morphology or vegetative life cycle. However, these NCA yeast showed strong impairments in sporulation and meiosis, including major meiotic delays and high rates of abnormal chromosome segregation. Our data indicate that the amino acid sequence of Nda2 is uniquely required for normal meiosis, and identify a novel determinant that underlies functional distinction between closely related tubulin isoforms.