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Updated: Sep 29, 2026

Exploring Sequence Space to Identify Binding Sites for Regulatory RNA-Binding Proteins
Published on: August 9, 2019
The RNA splicing factor ASF/SF2 inhibits human topoisomerase I mediated DNA relaxation
Félicie F Andersen1, Thomas Ø Tange, Thayaline Sinnathamby
1Department of Molecular and Structural Biology, University of Aarhus, C. F. Møllers Allé, Denmark.
Abstract:
Human topoisomerase I interacts with and phosphorylates the SR-family of RNA splicing factors, including ASF/SF2, and has been suggested to play an important role in the regulation of RNA splicing. Here we present evidence to support the theory that the regulation can go the other way around with the SR-proteins controlling topoisomerase I DNA activity. We demonstrate that the splicing factor ASF/SF2 inhibits relaxation by interfering with the DNA cleavage and/or DNA binding steps of human topoisomerase I catalysis. The inhibition of relaxation correlated with the ability of various deletion mutants of the two proteins to interact directly, suggesting that an interaction between the RS-domain of ASF/SF2 and a region between amino acid residues 208-735 on topoisomerase I accounts for the observed effect. Consistently, phosphorylation of the RS-domain with either topoisomerase I or a human cell extract reduced the inhibition of relaxation activity. Taken together with the previously published studies of the topoisomerase I kinase activity, these observations suggest that topoisomerase I activity is shifted from relaxation to kinasing by specific interaction with SR-splicing factors.
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