Abstract
Four different β-tubulin clones were isolated from carrot genomic and cDNA libraries. Their nucleotide sequences were determined1 and their predicted amino acids were compared with each other. The predicted amino acid composition of the C-terminal region of three of them (β-1, 3, 4) resembled one another, but that of one isotype (β-2) was divergent. The β-2 tubulin included two hydroxyl amino acids, serine and threonine, and consisted of a lower number of negatively charged amino acids than the others in the C-terminal region.
The predicted hydrophobicity profile of the β-2 tubulin around the residue 200 is less hydrophobic than β-1, but it is still more hydrophobic than those of animal and fungal β-tubulins. The β-2 gene was transcribed in cultured cells and flowers, while the β-1 gene was ubiquitously transcribed in cultured cells, roots, shoots and flowers.
When the predicted amino acids of plant tubulin were compared with those of other organisms, substitutions from non-polar amino acids to those with hydroxyl group were conspicuous in the region corresponding to the third exon in the plant genes.
