Table S1.

Isotype composition of isolated tubulins

Tubulin source	Tubulin Isotype (%)						Source
	βI	βII	βIII	βIV	βV	βVI
Bovine brain	3	58	25	13	ND	0	(18)
HeLa cells*	90	0	0	10	ND	0	(19)
Chicken erythrocytes	0	0	0	0	0	100	(20, 21)

Isotype composition of porcine brain tubulin is very similar to bovine brain tubulin (see Fig. S7). It should be noted that βI- and βII-tubulins have a very similar sequence, and it was found that the available βII-tubulin antibody cross-reacts with βI-tubulin (16). They are often grouped together (βI/βII). ND, not determined.

^*We have estimated that βIII-tubulin and βV-tubulin content in HeLa cells is ≤1% and ≤5%, respectively.