Comparison of proteolytic cleavage patterns of α-tubulins and β-tubulins from taxonomically distant species

The α and β-chains of tubulins from several taxonomically distant species were separated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and isolated by a procedure that avoided stains and acidic conditions. All the β-chains had the same electrophoretic mobility, but the α-chains of some of the lower eukaryotes migrated faster than the rest. Limited proteolytic digestion of the subunits with Staphylococcus aureus protease, followed by electrophoresis on 15% acrylamide gels, resulted in very similar peptide patterns for all the β-chains, but a variety of patterns for the α-chains. The peptide patterns of α-tubulins from sea urchin egg and sperm flagellar outer doublets were markedly different, whereas those of bovine brain and kidney were identical. Bovine and dogfish brain α-tubulin peptide patterns were also identical, in contrast to the very different one of squid brain. Strong similarities were found between the α-chain peptide patterns of sperm flagellar tubulin from the echiurid worm Urechis caupo and the sea urchins Lytechinus pictus and Strongylocentrotus purpuratus, indicating that functionally similar tubulins from very different species can be more closely related than functionally different tubulins from the same organism. Evidence for the evolution of plant sperm flagella from protistan flagella was provided by the distinctive and very similar α-chain peptide patterns of tubulin from sperm flagella of the bracken fern Pteridium aquilinum and the flagella of the unicellular biflagellate alga Chlamydomonas reinhardtii.