The Shape of Control: How Going in Circles Keeps RNA Catalytically Switched On

RNase P was one of the first enzymes discovered to have an RNA-based catalytic component. Since its identification, it has been extensively studied, particularly in E. coli , due to the ability of its M1 RNA to exhibit in vitro catalytic activity even in the absence of associated protein. In this study, we report G-quadruplex formation as a potential regulatory mechanism that modulates the catalytic activity of this RNA. We observed a significantly higher propensity for G-quadruplex formation in the linear isoform (linM1) compared to its circular counterpart (circM1). G-quadruplex formation was confirmed through circular dichroism spectroscopy and a fluorescence-based assay using a G-quadruplex-binding small molecule. We compared the catalytic activity of linM1 and circM1 in lithium and potassium environments and found that G-quadruplex formation specifically reduced linM1 activity. Furthermore, we observed distinct condensate properties of linM1 in the presence or absence of G-quadruplex structures. Overall, our findings suggest that G-quadruplex formation serves as a regulatory switch for RNA activity in linM1, whereas circM1 resists G-quadruplex formation and remains catalytically active even under conditions that favor G-quadruplex assembly.