AbstractIn many mammalian cell types, increases in the level of nonpolymerized tubulin cause an inhibition in tubulin synthesis which is accompanied by a decrease in tubulin mRNA levels. To see whether inhibition is caused by nuclear or cytoplasmic events, two groups have recently examined the ability of enucleated cells to autoregulate tubulin synthesis.1,2 These experiments have demonstrated that transcription, processing, and transport of tubulin mRNAs from the nucleus to the cytoplasm are not major sites of autoregulation. Instead, monomeric tubulin must reduce, either directly or indirectly, the translatability of its own message.