Figure 2.

RNA topoisomerase activity is prevalent in Type IA topoisomerases from all 3 domains of life. (A) Schematic representation of the RNA topoisomerase assay. A synthetic circular RNA substrate contains 2 pairs of complementary regions (red and green) separated by single-stranded spacers (black). Through strand passage reactions, this substrate is converted to a trefoil knot in which the 2 pairs of complementary regions can form normal double helices. (B) Schematic representation of the domain structures of Type IA topoisomerases from different species (left) and their RNA topoisomerase activity.^17,21,28,31 The conserved core domains and the non-conserved CTDs, including Zn-fingers (orange boxes), are indicated. Their RNA topoisomerase activity was shown on the right. Fig. 2A is adapted from Fig. 4 of the previous paper.¹⁷ Fig. 2B is adapted from 4 figures of another paper.²⁸