P2 functions as a spacer in the Tetrahymena ribozyme

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Group I introns are self-splicing RNA molecules.
• The P2 stem-loop is a conserved structural element in group I introns.
• Understanding P2's function is key to elucidating catalytic intron mechanisms.

Purpose of the Study:

• To investigate the functional role of the P2 stem-loop region in Tetrahymena thermophila group I introns.
• To analyze the impact of P2 stem mutations and length variations on catalytic activity.
• To assess the proposed coaxial stacking model of P1 and P2 stems.

Main Methods:

• Comprehensive mutation analysis of the P2 stem-loop.
• Varying the length of the P2 stem.
• Assessing intron-catalyzed cleavage activity and efficiency.
• Phylogenetic analysis of group I introns.

Main Results:

• The bottom base pair of the P2 stem and L2 loop nucleotides interact with other intron regions.
• P2 stem length is constrained to 9-11 base pairs.
• P2 length variation did not alter cleavage sites in P1, challenging coaxial stacking.
• Altering P2 length (insertion vs. deletion) reduced cleavage activity and efficiency.

Conclusions:

• The P2 stem-loop is essential for group I intron catalysis in Tetrahymena.
• Coaxial stacking of P1 and P2 stems is unlikely in this intron.
• P2 length changes likely disrupt the active site by altering P1 positioning, affecting cleavage.
• P2 interactions are critical for maintaining the precise architecture of the catalytic core.