A DEAD protein that activates intron self-splicing without unwinding RNA

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• Group II introns are mobile genetic elements requiring specific conditions for self-splicing.
• The protein Mss116 (a DExH/D protein) is known to assist ai5gamma intron splicing in vivo.
• In vitro studies typically require high salt and temperature for ai5gamma intron splicing.

Purpose of the Study:

• To investigate the in vitro function of Mss116 on group II intron ai5gamma splicing under physiological conditions.
• To explore the role of DEAD-box proteins in RNA tertiary structure assembly.
• To elucidate the mechanism by which Mss116 stimulates splicing.

Main Methods:

• In vitro splicing assays of the ai5gamma intron.
• Biochemical analysis of Mss116 and related DEAD-box proteins.
• Mutational analysis of Mss116 ATPase and helicase activities.

Main Results:

• Mss116 significantly stimulates ai5gamma splicing under near-physiological conditions in vitro.
• A subset of DEAD-box proteins also enhances ai5gamma splicing, suggesting a subfamily involved in RNA structure assembly.
• ATPase activity of Mss116 is essential for splicing stimulation, but helicase activity is not required.
• Mss116 likely stabilizes on-pathway intermediates rather than resolving kinetic traps.

Conclusions:

• Mss116 acts as an RNA chaperone, promoting efficient group II intron splicing by stabilizing crucial intermediates.
• DEAD-box proteins may play a broader role in RNA tertiary structure formation.
• The mechanism of Mss116 action involves ATPase activity for structural stabilization, not RNA unwinding.