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J. Biol. Chem., Vol. 263, Issue 31, 16023-16031, 11, 1988
MB Yaffe, GW Farr and H Sternlicht
We describe the in vitro expression and characterization of the isolated
beta-tubulin subunit in rabbit reticulocyte lysates and compare its
assembly and chromatographic properties with that of the isolated
alpha-subunit and the tubulin heterodimer. The beta-tubulin polypeptides,
derived from a single chicken beta-tubulin cDNA, were found in three
distinct molecular forms: a multimeric or lysate- associated form, beta I
(Mr approximately 180,000); the free beta- subunit beta II (Mr
approximately 55,000); and the hybrid heterodimer alpha(rabbit)
beta(chick), beta III (Mr approximately 80,000-100,000). The hybrid
heterodimers were 100% assembly competent, whereas beta- tubulin in the
"associated" beta I and the monomeric beta II forms displayed only
approximately 70 +/- 15 and 25 +/- 10% competence, respectively, in
coassembly assays with bovine brain tubulin. This reduced functionality was
not a consequence of diminished beta-subunit stability or protein
denaturation. By comparing the elution positions of the three beta forms,
the monomeric alpha-subunit, and tubulin dimer purified from bovine brain,
we demonstrate that anion-exchange columns (Mono-Q) interact preferentially
with the alpha-subunit and chromatograph tubulin dimer on the basis of
alpha-subunit isotype. The rate of exchange of the free beta-subunit into
bovine tubulin dimer was followed chromatographically. The exchange was
slow at 4 degrees C and rapid at 37 degrees C where it is essentially
complete in 40 min in the presence of 2.5 mg/ml bovine microtubule protein.
Exogenous GTP, a potent effector of microtubule assembly, binds
exchangeably to beta II and enhances the recovery of this form from the
Mono-Q column, suggesting that GTP binding may occur at identical sites in
the isolated beta-subunit and in the tubulin heterodimer.
Translation of beta-tubulin mRNA in vitro generates multiple molecular forms
Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106.
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