Unveiling the intriguing role of FAP20 in tubulin recruitment at the doublet microtubule inner junctions

In this issue of Structure, Bangera et al. investigate the role of the inner junction protein FAP20 in doublet microtubule assembly. Using cryo-EM and microtubule dynamic assays, they demonstrate that FAP20 re-cruits free tubulins to existing microtubule lattices, shedding light on B-tubule closure during doublet micro -tubule formation.