Contributions of phylogenetically variable structural elements to the function of the ribozyme ribonuclease P

Area of Science:

• Molecular Biology
• Enzymology
• RNA structure and function

Background:

• Ribonuclease P (RNase P) is a ribonucleoprotein enzyme essential for precursor tRNA processing.
• The catalytic activity resides in the RNA subunit, independent of the protein subunit.
• Bacterial RNase P RNAs feature a conserved core with variable helical elements, whose functional significance is debated.

Purpose of the Study:

• To investigate the specific roles of four variable helical elements in Escherichia coli RNase P RNA.
• To determine if these elements contribute to RNA folding, stability, or substrate binding.
• To elucidate the functional impact of deleting these variable elements.

Main Methods:

• Site-directed mutagenesis to delete individual helical elements from E. coli RNase P RNA.
• In vitro assays to measure RNase P activity, RNA folding under varying salt concentrations, and substrate binding affinity.
• Temperature sensitivity assays to assess structural stability.

Main Results:

• Deletion of one element had no discernible effect on RNase P activity.
• Two elements are critical for correct RNA folding, necessitating high salt concentrations for stability in their absence.
• The fourth element forms a pseudoknot, contributing to structural stability and substrate binding; its absence leads to temperature sensitivity and a 100-fold increase in KM.

Conclusions:

• Variable helical elements in E. coli RNase P RNA possess specific, non-redundant functions.
• These elements are essential for optimal RNA folding, structural integrity, and efficient substrate recognition.
• The findings challenge the notion that variable elements are merely evolutionary modifications with no critical role.