Talk abstracts

Talk on Friday 01:00-01:15pm submitted by Daniel Totten

Antagonistic splicing factors hnRNP A1 and SRSF2 compete for binding to snRNA 7SK

Daniel C. Totten (Department of Biological Sciences, University of Pittsburgh), Andrea J. Berman (Department of Biological Sciences, University of Pittsburgh)

Transcription of protein-coding genes in metazoans is tightly regulated through controlled pausing and restarting of RNA polymerase II enforced by P-TEFb, a critical transcription factor1. P-TEFb is regulated through the reversible association with the snRNA 7SK and the 7SK-P-TEFb RNP, a ribonucleoprotein, which includes SRSF22. Upon P-TEFb dissociation from this RNP, 7SK RNA binds to several hnRNPs and forms the 7SK-hnRNP RNP3. To better understand the maintenance of these mutually exclusive RNPs, we investigated the binding of hnRNP A1 and SRSF2 to Stem III of 7SK RNA. We show for the first time that the RNA binding domains of hnRNP A1 melt Stem III and bind to its 3’ half with modest affinity, whereas the single RNA binding motif of SRSF2 is unable to open Stem III to access its binding sites and results in a 10-fold lower affinity for Stem III. Further, hnRNP A1 and SRSF2 efficiently compete and occlude binding by the competitor protein upon saturating conditions; both proteins bind the same RNA molecule when lower concentrations of proteins are used. However, SRSF2 is only efficiently recruited from Stem III to a competing RNA in the presence of UP1, suggesting a model in which hnRNP A1 and SRSF2 help maintain mutually exclusive RNPs through occlusion of the competitor protein, yet work together to aid in the transition between the two 7SK RNPs.

1. Guo, J. and D.H. Price, RNA polymerase II transcription elongation control. Chem Rev, 2013. 113(11): p. 8583-603.
2. Ji, X., et al., SR proteins collaborate with 7SK and promoter-associated nascent RNA to release paused polymerase. Cell, 2013. 153(4): p. 855-868.
3. Diribarne, G. and O. Bensaude, 7SK RNA, a non-coding RNA regulating P-TEFb, a general transcription factor. RNA Biol, 2009. 6(2): p. 122-8.

Keywords: 7SK RNA, hnRNP A1, SRSF2