Possible regulation of microtubules through destabilization of tubulin.

Chaperones and folding cofactors are known to mediate posttranslational folding of nascent tubulin, thus forming functional dimers. Based on sequence likeness, a novel protein similar to cofactor E, E-like protein (El), was identified. In overexpression experiments El, similar to a subset of folding factors (i.e. cofactors D and E), appears to disrupt functional dimers and target them for destruction by the proteasome. El apparently does not interact with microtubules directly and has no function in the tubulin folding pathway. Suppression of El expression seems to increase the cellular content of stable, posttranslationally modified microtubules by an unknown mechanism. Degradation of functional tubulin dimers as well as the alteration of the cellular content of stable microtubules through El might regulate the distribution and organization of organelles in vivo.