CNPase is a myelin-associated enzyme that makes up 4% of total CNS myelin protein, and is thought to undergo significant age-associated changes. It is named for its ability to catalyze the phosphodiester hydrolysis of 2',3'-cyclic nucleotides to 2'-nucleotides. CNPase is expressed exclusively by oligodendrocytes in the CNS, and the appearance of CNPase seems to be one of the earliest events of oligodendrocyte differentiation. CNPase is thought to play a critical role in the events leading up to myelination. CNPase also associates with microtubules in brain tissue and FRTL-5 thyroid cells, and is reported to have microtubule-associated protein-like activity, being able to catalyze microtubule formation at low molar ratios. Deletion of the C-terminus of CNPase or phosphorylation abolish the catalytic activity of microtubule formation. CNPase can link tubulin to cellular membranes, and might be involved in the regulation cytoplasmic microtubule distribution.