Decoding the Complex Functional Landscape of the ykkC Riboswitches.

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• The ykkC riboswitch class exhibits remarkable diversity in ligand recognition despite minor sequence and structural variations.
• Previous structural studies elucidated sequence-structure relationships but lacked functional insights into riboswitch specificity.

Purpose of the Study:

• To investigate the functional role of the ppGpp riboswitch variant in transcriptional control using extensive mutational analysis.
• To define the requirements for functional riboswitch specificity and explore ligand-binding variations within the ykkC class.

Main Methods:

• Extensive mutational analysis of the ppGpp riboswitch.
• Disruption of the terminator hairpin at a single base pair.
• Phylogenetic analysis of natural ykkC riboswitches.

Main Results:

• Disrupting a single base pair in the terminator hairpin abolished nearly all riboswitch function, indicating critical fine-tuning.
• Mutational analysis indicated that G93 is not exclusively linked to PRPP-driven function.
• Phylogenetic analysis identified a novel ykkC subclass binding both XMP and GMP, associated with de novo GMP synthesis genes.

Conclusions:

• Riboswitch fine-tuning, particularly of the terminator hairpin, is essential for function and suggests broad tunability across riboswitches.
• The discovery of a new ykkC subclass binding XMP and GMP provides evidence that small sequence changes can significantly alter ligand specificity.