title: Interactions between the tetratricopeptide repeat-containing transcription factor TFIIIC131 and its ligand, TFIIIB70. Evidence for a conformational change in the complex.
abstract: In the transcription of tRNA and 5 S genes by RNA polymerase III, recruitment of the transcription factor (TF)IIIB is mediated by the promoter-bound assembly factor TFIIIC. A critical limiting step in this process is the interaction between the tetratricopeptide repeat (TPR)-containing subunit of TFIIIC (TFIIIC131) and the TFIIB-related factor Brf1p/TFIIIB70. To facilitate biochemical studies of this interaction, we expressed a fragment of TFIIIC131, TFIIIC131-(1-580), that includes the minimal TFIIIB70 interaction domain defined by two-hybrid studies together with adjacent sequences, up to the end of TPR9, implicated in the assembly reaction. TFIIIC131-(1-580) interacts with TFIIIB70 in solution and inhibits the formation of TFIIIB70.TFIIIC.DNA complexes. In a coupled equilibrium binding assay, the formation of TFIIIC131-(1-580).TFIIIB70 complexes was adequately described by a single-site binding model and yielded an apparent equilibrium dissociation constant of 334 +/- 23 nm. CD spectroscopy and limited proteolysis experiments defined a well structured and largely protease-resistant core in TFIIIC131-(1-580) comprising part of the hydrophilic amino terminus, TPR1-5, the intervening non-TPR region, and TPR6-8. CD spectra showed that trifluoroethanol induced significant alpha-helical structure in TFIIIC131-(1-580). A more modest monovalent ion-dependent CD difference was observed in mixtures of TFIIIC131-(1-580) and TFIIIB70, suggesting that formation of the binary complex may proceed with the acquisition of alpha-helicity.
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: R D
authors.initials: RD
authors.lastname: Moir
authors.forename: K V
authors.initials: KV
authors.lastname: Puglia
authors.forename: I M
authors.initials: IM
authors.lastname: Willis
mesh_terms: D000123:Acetyltransferases / Q000378:metabolism*; D002942:Circular Dichroism; D004258:DNA Polymerase III / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry; D010446:Peptide Fragments / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D035361:Transcription Factor TFIIIB; D014157:Transcription Factors / Q000378:metabolism*; D019474:Transcription Factors, TFIII / Q000378:metabolism*; D014158:Transcription, Genetic; D015003:Yeasts; D000098832:Transcription Factor TFIIIC
chemical_list: D005656:Fungal Proteins; D010446:Peptide Fragments; D035361:Transcription Factor TFIIIB; D014157:Transcription Factors; D019474:Transcription Factors, TFIII; D000098832:Transcription Factor TFIIIC; D000123:Acetyltransferases; D004258:DNA Polymerase III