TAF9b (Formerly TAF9L) Is a Bona Fide TAF That Has Unique and Overlapping Roles with TAF9

Abstract

TFIID plays a key role in transcription initiation of RNA polymerase II preinitiation complex assembly. TFIID is comprised of the TATA box binding protein (TBP) and 14 TBP-associated factors (TAFs). A second set of transcriptional regulatory multiprotein complexes containing TAFs has been described (called SAGA, TFTC, STAGA, and PCAF/GCN5). Using matrix-assisted laser desorption ionization mass spectrometry, we identified a novel TFTC subunit, human TAF9Like, encoded by a TAF9 paralogue gene. We show that TAF9Like is a subunit of TFIID, and thus, it will be called TAF9b. TFIID and TFTC complexes in which both TAF9 and TAF9b are present exist. In vitro and in vivo experiments indicate that the interactions between TAF9b and TAF6 or TAF9 and TAF6 histone fold pairs are similar. We observed a differential induction of TAF9 and TAF9b during apoptosis that, together with their different ability to stabilize p53, points to distinct requirements for the two proteins in gene regulation. Small interfering RNA (siRNA) knockdown of TAF9 and TAF9b revealed that both genes are essential for cell viability. Gene expression analysis of cells treated with either TAF9 or TAF9b siRNAs indicates that the two proteins regulate different sets of genes with only a small overlap. Taken together, these data demonstrate that TAF9 and TAF9b share some of their functions, but more importantly, they have distinct roles in the transcriptional regulatory process.

ACKNOWLEDGMENTS

We are grateful to M. Oulad-Abdelghani for generating specific TAF9 and TAF9b antibodies, to E. Martinez and R. G. Roeder for the polyclonal antibody that recognizes both TAF9 and TAF9b, to I. Kolb-Cheynel for help with the recombinant baculoviruses, to P. Schultz and C. Ruhlman for the EM study, to A. Jànoshàzi for training to do the FRET experiments, and to T. Hilton, M. Demény, S. Brancorsini, and N. Clarke for critical reading of the manuscript. We also thank the IGBMC cell culture facility for providing cells.

M.F. is supported by a European Community Marie Curie individual fellowship (MEIF-CT-2003-501146), and E.S. is supported by an EMBO long-term fellowship. This work was supported by funds from INSERM, CNRS, Hôpital Universitaire de Strasbourg, Association pour la Recherche sur le Cancer, the Fondation pour la Recherche Médicale, the Font Nationale de La Science ACI, INTAS (01-0211), and European Community RTN (HPRN-CT-2000-00087, HPRN-CT-2000-00088, and HPRN-CT-2004-504228), STREP (LSHG-CT-2004-502950), and AICR (03-084) grants.