Transcription termination factor TTF-I exhibits contrahelicase activity during DNA replication.
In mammals, sequence-specific termination of DNA replication within the ribosomal RNA genes is catalyzed by a defined DNA-protein complex that includes transcription termination factor I (TTF-I). Here we show that TTF-I acts as a polar contrahelicase contrary to the intrinsic 3' -->5' helicase activity of SV40 large T antigen. The contrahelicase activity requires binding of TTF-I to its cognate recognition site and the presence of an auxiliary GC-rich sequence, which is able to form a specific secondary structure. Mutations in the GC-rich sequence lead to a loss of folding into correct secondary structure and abrogate contrahelicase activity. The finding suggests that a specific interaction between the Sal box-bound TTF-I and the GC-rich sequence is essential for the inhibition of T antigen helicase. Analyses of N-terminally truncated mutants of TTF-I showed inhibition of helicase by the same domain of TTF-I, which is also responsible for replication fork arrest.
Putter
Vera
V
Institute of Biochemistry, University of Würzburg, D-97074 Würzburg, Germany.
Grummt
Friedrich
F
D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000502:physiology; D001426:Bacterial Proteins; D002460:Cell Line; D004261:DNA Replication / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation
D000952:Antigens, Polyomavirus Transforming; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C063112:rtP protein, Bacillus subtilis