A wealth of data is now available on primary structures
of various tubulins. Higher eukaryotes contain multiple
genes for 0~- and 13-tubulin (five and six, respectively, in
chicken) [3], and there has been a long-standing question
of whether different tubulin isotypes serve different
functions (reviewed by Cleveland, J Cell Biol 1987,
104:381-383). While this may be true in some cases (e.g.
the microtubules of the marginal band of avian erythrocytes),
several recent studies show that different tubulins
copolymerize indiscriminately [4,5]. Thus the role of
tubulin diversity remains open. The main region of divergence
is near the C-termini of 0t- and 13-tubulin; other
areas occur close to the N-terminus. Since the C-terminal
regions are highly antigenic they provide suitable epitopes
for generating isotype-specific antibodies.
Since tubulin binds GTP, and since the sequences of various
G-proteins as well as two X-ray structures are now
known (reviewed in [6]), there is a possibility that the
folding of the tubulin chain could be predicted. The potential
nucleotide interaction sites of tubulin are likely to