An enzyme tyrosylating α-tubulin and its role in microtubule assembly

Summary Alpha tubulin is shown to be the only polypeptide in brain extracts which undergoes C-terminal addition of a tyrosine residue. Tubulin purified by cycles of in vitro polymerization can be used as substrate to assay and purify the tyrosine ligase. Tubulin dimer is a substrate for the enzyme and axonemal doublet microtubules are not. Both tyrosylated and untyrosylated dimers can polymerize in vitro .