Structural
and functional interactions between RNA polymerase II and its elongation
factors.
Elena Shematorova (1), Pierre Thuriaux (1), Maxime Wéry (2), Benoît Van Driessche
(2), Jean Vandenhaute (2), Vincent Van Mullem (2)
(1) Département de SBGM, CEA/Saclay, Bât 144, Gif-sur-Yvette, 91191, France
(elenashe@matthieu.saclay.cea.fr); (2) Laboratoire de Génétique Moléculaire
(URBM), Facultés Universitaires Notre-Dame de la Paix. 61, rue de Bruxelles,
B-5000 Namur (Belgique).
We are
interested in the structural and functional interactions relating RNA
polymerase II (Pol II) to its elongation factors. Using a two-hybrid approach,
we showed that the transcript cleavage factor TFIIS (encoded by PPR2 in Saccharomyces
cerevisiae)
interacts with two components of the transcription machinery, Spt8 and Srb9.
Srb9 belongs to an inhbitory module of the Pol II Mediator. Mutants with a
truncated CTD are suppressed by srb9-Δ and lethal in ppr2-Δ, indicating antagonistic
effects of Srb9 and TFIIS. Spt8 belongs to the SAGA coactivator. spt8-Δ and ppr2-Δ are sensitive to
nucleotide depleting drugs, have parallel effects on SAGA mutants and are
epistatic to mutants lacking the non-essential Pol II subunit Rpb9, suggesting
that their elongation defects are mediated by Rpb9. In contrast, spt8-Δ, rpb9-Δ and ppr2 mutants lacking the
N-terminal domain of TFIIS are lethal when lacking the other non-essential
subunit, Rpb4, suggesting that Pol II adopts a cleavage dependent configuration
in the absence of that subunit. Thus the two non-essential subunits of Pol II,
Rpb9 and Rpb4, have contrasting effects on the cleavage and elongation
properties of the enzyme. We are currently exploring the genetic effect of
other components of the SAGA complex on Pol II mutants affecting elongation.