Talk Abstracts

Talk on Saturday 08:30-08:45am submitted by Avleen Chawla

Going in circles, staying in control: How circRNA helps bacteria weather stress

Avleen K. Chawla (Carnegie Mellon University), Mary J. Billings (Carnegie Mellon University), Anna M. Kietrys (Carnegie Mellon University)

Abstract:
RNase P was among the first enzymes identified to harbor an RNA-based catalytic component¹. Since its discovery, it has been studied extensively, particularly in E. coli, as its M1 RNA retains catalytic activity in vitro even without the protein subunit². Herein, we report two bacterial firsts: the identification of a circular RNA isoform of M1 (circM1), and the discovery of a functional G-quadruplex (rG4) structure that regulates RNA catalysis. We found that the linear isoform (linM1) exhibits a significantly higher propensity for G-quadruplex formation compared to circM1. rG4 structures were validated using circular dichroism spectroscopy and a fluorescence assay with NMM, a G-quadruplex-binding small molecule. Functional assays in lithium- and potassium-rich environments revealed that G-quadruplex formation specifically diminishes linM1 activity, while circM1 resists rG4 assembly and remains catalytically active. Moreover, linM1 displayed distinct condensate-forming behaviors depending on the presence or absence of G-quadruplexes. Together, these findings establish both the first circRNA and the first functional G-quadruplex in bacteria, uncovering a novel regulatory switch for RNA catalysis and revealing circularization as a strategy to evade G-quadruplex inhibition.

References:
1. Guerrier-Takada, C., Gardiner, K., Marsh, T., Pace, N. & Altman, S. The RNA moiety of ribonuclease P is the catalytic subunit of the enzyme. Cell 35, 849–857 (1983).
2. Zhu, J. et al. Structural and mechanistic basis for recognition of alternative tRNA precursor substrates by bacterial ribonuclease P. Nature Communications 2022 13:1 13, 1–13 (2022).

Keywords: circRNA, RNase P, G-quadruplex