Cilia and flagella are essential eukaryotic organelles composed of an evolutionary conserved structure of 9 doublet microtubules that are similar but not equivalent. We propose that a tubulin post-translational modification called glutamylation could act as a tubulin code defining the molecular identity of each microtubule and governing its interactions with associated proteins. This project aims at investigating in detail this particular tubulin code, its biological significance and the way the cells can read it using the protist Trypanosoma brucei as model. First, the complexity of tubulin glutamylation of flagellar microtubules will be deciphered to an unprecedented level using advanced mass spectrometry. Second, the importance of glutamylation will be worked out by either replacement of glutamylases with enzymatically inactive versions or targeted expression of deglutamylases in the flagellum. Finally, the ability of molecular motors to read the tubulin code will be investigated using novel in vitro assays.