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Updated: Apr 7, 2026

Analysis of Termination of Transcription Using BrUTP-strand-specific Transcription Run-on TRO Approach
Published on: March 12, 2017
Poly(A) Signal-Dependent Transcription Termination Occurs through a Conformational Change Mechanism that Does Not
Huimin Zhang1, Frank Rigo2, Harold G Martinson1
1Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA.
Abstract:
Transcription termination for genes encoding polyadenylated mRNAs requires a functional poly(A) signal (PAS) in the nascent pre-mRNA. Often called PAS-dependent termination, or PADT, it is widely assumed that the PAS requirement reflects an obligatory poly(A) site cleavage requirement for termination. Cleavage is thought to provide entry for a 5'-to-3' exonuclease that targets RNA polymerase II via the nascent transcript-i.e., the torpedo model. To assess the role of cleavage in PADT, we developed a PADT assay using HeLa nuclear extract. Here we examine the basal mechanism of PADT and show that cleavage at the poly(A) site is not required for PADT. Isolated elongation complexes undergo termination in a PAS-dependent manner when incubated in buffer, in the absence of extract, nucleotides, or cleavage at the poly(A) site. Thus, PADT-proficient complexes undergo a conformational change that triggers termination. PADT is inhibited by α-amanitin, which presumably blocks the required conformational change.
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