Important 2'-hydroxyl groups within the core of a group I intron

Area of Science:

• Molecular Biology
• Biochemistry
• RNA Catalysis

Background:

• Group I introns are catalytic RNA molecules essential for gene expression.
• Their catalytic core, often shielded from solvent, requires structural investigation.
• A bimolecular reaction system was developed to study intron core structure and function.

Purpose of the Study:

• To investigate the role of ribose sugars in the J8/7 region of a group I intron.
• To elucidate the contribution of the ribose phosphate backbone to catalytic activity.
• To analyze the impact of specific nucleotide substitutions on splicing efficiency.

Main Methods:

• Development of an efficient bimolecular reaction system for kinetic analysis.
• Systematic substitution of ribose sugars with deoxyribose in the J8/7 region and P7 helix.
• Kinetic analysis of splice-site cleavage and GTP-independent hydrolysis.

Main Results:

• Multiple deoxyribonucleotide substitutions in J8/7 completely blocked 5'-splice-site cleavage, indicating the backbone's catalytic role.
• Individual substitutions at G303 and A306 reduced catalysis rates 5-10 fold, with G303 blocking GTP-independent hydrolysis.
• Deoxyribonucleotide substitutions in the 3'-section of P7 significantly reduced catalytic efficiency (kcat/Km).

Conclusions:

• The ribose phosphate backbone of J8/7 is critical for group I intron catalytic activity.
• Specific nucleotides within J8/7 and P7 play important roles in catalysis and substrate binding.
• The bimolecular system provides a valuable tool for dissecting the catalytic mechanisms of group I introns.