Reduced Sensitivity to RNA Structural Differences Distinguishes Eukaryotic Pus4 from Bacterial TruB

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• Pseudouridine (Ψ) is a crucial RNA modification affecting RNA structure and function.
• Pseudouridine synthases (Pus) catalyze the isomerization of uridine (U) to Ψ.
• While all Pus enzymes modify non-coding RNAs, some also modify messenger RNAs (mRNAs), impacting gene expression.

Purpose of the Study:

• To investigate the mechanisms of mRNA target selection by Pus enzymes.
• To compare the substrate specificity of Saccharomyces cerevisiae Pus4 and bacterial TruB.
• To understand how RNA secondary structure influences Pus enzyme activity.

Main Methods:

• In vitro binding and modification assays using structurally diverse RNA substrates.
• Comparative enzymatic activity analysis of Pus4 and TruB.
• Investigation of the role of the PUA domain in substrate selection.

Main Results:

• Yeast Pus4 binds and modifies RNAs with secondary structures distinct from its canonical tRNA targets.
• Both Pus4 and TruB exhibit promiscuous in vitro activity, but Pus4 is more robust.
• The bacterial PUA domain influences TruB's substrate selection, while Pus4's selection may involve additional cellular factors.

Conclusions:

• Pus4's substrate selection for mRNA modification is not solely based on mimicking tRNA structures.
• Enzyme activity in vitro may not fully reflect in vivo substrate specificity.
• Additional cellular factors likely contribute to Pus4's precise mRNA target recognition.