TATA BOX-BINDING PROTEIN (TBP) IS A CONSTITUENT OF THE POLYMERASE I-SPECIFIC TRANSCRIPTION INITIATION-FACTOR TIF-IB (SL1) BOUND TO THE RIBOSOMAL-RNA PROMOTER AND SHOWS DIFFERENTIAL SENSITIVITY TO TBP-DIRECTED REAGENTS IN POLYMERASE-I, POLYMERASE-II, AND POLYMERASE-III TRANSCRIPTION FACTORS

The role of the Acanthamoeba castellanii TATA-binding protein (TBP) in transcription was examined. Specific antibodies against the nonconser ved N-terminal domain of TBP were used to verify the presence of TBP i n the fundamental transcription initiation factor for RNA polymerase I , TIF-IB, and to demonstrate that TBP is part of the committed initiat ion complex on the rRNA promoter. The same antibodies inhibit transcri ption in all three polymerase systems, but they do so differentially. Oligonucleotide competitors were used to evaluate the accessibility of the TATA-binding site in TIF-IB, TFIID, and TFIIIB. The results sugge st that insertion of TBP into the polymerase II and III factors is mor e similar than insertion into the polymerase I factor.