Structural basis of a ribozyme's thermostability: P1–L9 interdomain interaction in RNase P RNA

For stability, many catalytic RNAs rely on long-range tertiary interactions, the precise role of each often being unclear. Here we demonstrate that one of the three interdomain architectural struts of RNase P RNA (P RNA) is the key to activity at higher temperatures: disrupting the P1–L9 helix–tetraloop interaction in P RNA of the thermophile Thermus thermophilus decreased activity at high temperatures in the RNA-alone reaction and at low Mg 2+ concentrations in the holoenzyme reaction. Conversely, implanting the P1–P9 module of T. thermophilus in the P RNA from the mesophile Escherichia coli converted the latter RNA into a thermostable one. Moreover, replacing the E. coli P1–P9 elements with a pseudoknot module that mediates the homologous interaction in Mycoplasma P RNAs not only conferred thermostability upon E. coli P RNA but also increased its maximum turnover rate at 55°C to the highest yet described for a P RNA ribozyme.