A tubulin-specific cDNA clone was isolated, using anti-chicken brain beta-tubulin monoclonal antibody as a probe, from a lambda gtll library of cDNA prepared from cultured carrot cells. It included a coding region of the C-terminal 39 amino acids and a part of the 3'-flanking of a beta-tubulin mRNA. The predicted amino acid sequence of 17 residues in the C-terminal variable region was AspGluGluGluTyrTyrGluAspGluGluGluGluGluAlaGlnGlyMet. Twenty-two amino acids preceding this acidic terminus were completely identical with those of the other known beta-tubulins, but the codons for them included many silent substitutions.