RNA helicase dynamics in pre-mRNA splicing.

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Pre-mRNA splicing involves complex molecular machinery, including the spliceosome.
• The DExH-box NTPase/helicase Prp22p is essential for releasing mature mRNA from the spliceosome post-splicing.
• Prp22p's dual roles in promoting the second transesterification and catalyzing mRNA release are critical for gene expression.

Purpose of the Study:

• To investigate the functional importance of Prp22p's helicase activity in pre-mRNA splicing.
• To understand how mutations affecting NTPase and helicase activities impact Prp22p function in vitro and in vivo.
• To explore the relationship between RNA unwinding and spliceosome disassembly using suppressor analysis.

Main Methods:

• Site-directed mutagenesis of Prp22p, specifically targeting motif III (SAT) residues S635 and T637.
• Biochemical assays to assess ATP hydrolysis, RNA unwinding, and mRNA release from the spliceosome.
• In vivo growth assays to evaluate the effects of mutations at different temperatures.
• Isolation and characterization of intragenic suppressors of the prp22-S635A mutation.

Main Results:

• Mutations S635A and T637A retained ATP hydrolysis but were deficient in unwinding duplex RNA and releasing mRNA.
• The prp22-S635A mutation caused temperature-sensitive lethality and slow growth in vivo.
• An intragenic suppressor mutation (V539I in motif Ia) restored helicase activity and mRNA release capability to the S635A mutant.

Conclusions:

• Prp22p's helicase activity is indispensable for efficient mRNA release from the spliceosome.
• There is a strong correlation between RNA unwinding by Prp22p and the disassembly of the spliceosome.
• Suppressor analysis provides a powerful approach to dissecting the intricate dynamics of helicase function in splicing.