THE AMINO-TERMINAL DOMAIN OF THE TRANSCRIPTION TERMINATION FACTOR TTF-I CAUSES PROTEIN OLIGOMERIZATION AND INHIBITION OF DNA-BINDING

The transcription termination factor TTF-I binds specifically to an 18 bp DNA element in the murine ribosomal gene spacer and mediates termi nation of RNA polymerase I transcription, In this study, we have compa red DNA binding and termination activity of recombinant full-length TT F-I (TTF-I-p130) with two deletion mutants lacking 184 and 322 N-termi nal amino acids, respectively, All three proteins exhibit similar term ination activity, but the DNA binding of TTF-I-p130 is at least one or der of magnitude lower than that of the deletion mutants, indicating t hat the N-terminus represses the interaction of TTF-I with DNA, The in hibitory effect of the N-terminus can be transferred to a heterologous DNA binding domain and is separable from other activities of TTF-I. W e show by several methods that TTF-I-p130, the N-terminal domain alone , and fusions of the N-terminus with the DNA binding domain of Oct2.2 form stable oligomers in solution, Thus, in contrast to previous studi es suggesting that activation of TTF-l occurs through proteolysis, we demonstrate that full-length TTF-l mediates termination of rDNA transc ription in vivo and in vitro and that the oligomerization state of TTF -I may influence its DNA binding activity.