Azouzi, C.; Schwank, K.; Queille, S.; Kwapisz, M.; Aguirrebengoa, M.; Henras, A.; Lebaron, S.; Tschochner, H.; Lesne, A.; Beckouet, F.; Gadal, O.; DEZ, c.

The RNA polymerase I (Pol I) enzyme that synthesizes large rRNA precursors, exhibits high rate of pauses during elongation, indicative of a discontinuous process. We propose here that Premature Termination of Transcription (PTT) by Pol I is a critical regulatory step limiting rRNA production in vivo. The Pol I mutant, SuperPol (RPA135-F301S), produces 1.5-fold more rRNA than the wild type (WT). Combined CRAC and rRNA analysis link increased rRNA production in SuperPol to reduced PTT, resulting in shifting polymerase distribution toward the 3-prime end of rDNA genes. In vitro, SuperPol shows defective nascent transcript cleavage. Notably, SuperPol is resistant to BMH-21, a drug impairing Pol I elongation and inducing proteasome-mediated degradation of Pol I subunits. Compared to WT, SuperPol maintains subunit stability and sustains high transcription levels upon BMH-21 treatment. These comparative results show that PTT is alleviated in SuperPol while it is stimulated by BMH-21 in WT Pol I.