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 i n the amount of alpha- and beta-tubulin mRNAs is observed as analyzed by Northern blot hybridization using the homologous genomic tubulin pr obes. Between 60 and 120 min after the onset of reciliation, tubulin t ranscripts 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 t ubulin genes. The results obtained show that the apparent tubulin gene transcription rate is increased in reciliating cells from 15 min up t o 90 min. The block of transcription using actinomycin D shows that hs ps are not implicated in the destabilization of tubulin mRNA during th e first minutes of reciliation. The effects of the inhibitors of prote in synthesis, cycloheximide and pactamycin, on tubulin mRNA levels sug gest that the translational apparatus plays a role in the stability of tubulin mRNA in cells reciliating for 15 and 30 min. Experiments usin g 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.