The mechanisms of tubulin messenger regulation during Tetrahymena pyriformis reciliation.

The reciliation of Tetrahymena pyriformis cells is accompanied in the first minutes by a transient induction of stress mRNAs, i.e. hsp70 and ubiquitin. At the same time an accentuated and coordinate reduction in the amount of alpha- and beta-tubulin mRNAs is observed as analyzed by Northern blot hybridization using the homologous genomic tubulin probes. Between 60 and 120 min after the onset of reciliation, tubulin transcripts in the cytoplasm reach higher values than in exponentially growing cells. Run-on transcription assays reveal that the decrease in tubulin mRNA levels is not caused by a decrease in transcription of tubulin genes. The results obtained show that the apparent tubulin gene transcription rate is increased in reciliating cells from 15 min up to 90 min. The block of transcription using actinomycin D shows that hsps are not implicated in the destabilization of tubulin mRNA during the first minutes of reciliation. The effects of the inhibitors of protein synthesis, cycloheximide and pactamycin, on tubulin mRNA levels suggest that the translational apparatus plays a role in the stability of tubulin mRNA in cells reciliating for 15 and 30 min. Experiments using the microtubule-polymerizing drug taxol also show that tubulin mRNA destabilization is not a simple consequence of a temporary increase in free tubulin subunit pools resulting from cilia resorption.