Tubulin, a fundamental building block of the microtubule cytoskeleton, is an essential protein whose cellular levels are precisely controlled. One key regulatory pathway is tubulin autoregulation—a post-transcriptional mechanism that selectively degrades tubulin mRNA in response to an excess of unassembled tubulin. In this pathway, the specificity factor TTC5 recognizes nascent tubulin on the translating ribosome and, via the adaptor protein SCAPER, recruits the CCR4-NOT deadenylase complex to trigger mRNA decay. While the ribosome-associated mechanism has been understood in detail, how is this pathway regulated upstream to prevent aberrant activity when tubulin is not elevated remained unknown.

This doctoral thesis addresses this gap by identifying soluble αβ-tubulins as key upstream factor that reversibly sequesters TTC5. In steady-state conditions, TTC5 remains inactive in complex with αβ-tubulins, but when free tubulin levels rise, it dissociates and binds tubulin-translating ribosomes to initiate mRNA decay. The precise regulation of TTC5 is critical, as both loss-of-function and constitutively active TTC5 mutants cause severe impairment in mitosis.

Furthermore, this work established novel tools to study tubulin autoregulation and investigated the pathway systematically by a genome-wide CRISPR/Cas9 screen. The screen robustly identified core pathway components and revealed possible novel regulators. Collectively, this thesis provides a model for TTC5 upstream regulation, a powerful toolkit for future work, and a rich dataset to explore the open questions in tubulin autoregulation field.