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Updated: Aug 19, 2026

Analysis of RNA Processing Reactions Using Cell Free Systems: 3' End Cleavage of Pre-mRNA Substrates in vitro
Published on: May 3, 2014
EM visualization of transcription by RNA polymerase II: downstream termination requires a poly(A) signal but not
Y N Osheim1, N J Proudfoot, A L Beyer
1University of Virginia Health Sciences Center, Department of Microbiology, Charlottesville 22908, USA.
Abstract:
We have used EM visualization of active genes on plasmid vectors in Xenopus oocyte nuclei to investigate the relationship between poly(A) signals and RNA polymerase II transcription termination. Although a functional poly(A) signal is required for efficient termination, cotranscriptional RNA cleavage at the poly(A) site is not. Furthermore, the phenomena of termination and cotranscriptional RNA cleavage can be uncoupled, and the efficiency of both varies independently on different copies of the same plasmid template in the same oocyte nucleus. The combined observations are consistent with a scenario in which there is template-specific addition to Pol II (presumably at the promoter) of elongation and/or RNA processing factors, which are altered upon passage through a poly(A) signal, resulting in termination and, in some cases, cotranscriptional RNA cleavage.
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