Most of the mRNA sequences coding for alpha and beta tubulin in embryonic chick brain have been determined by sequencing of cloned cDNA copies of these mRNA copies of these mRNAs. From a 1,682-base pair cDNA sequence we have deduced the entire protein sequence for beta tubulin. For alpha tubulin, all but about 38 N-terminal amino acids have been deduced from the cDNA sequence. Although tyrosine has previously been shown to be post-translationally added to the C-terminus of alpha tubulin by a specific ligase, we conclude that the primary post-translational even must be the removal, not the addition of tyrosine because a terminal tyrosine is encoded by the mRNA.