The Spliceosome: A Protein-Directed Metalloribozyme

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Pre-mRNA splicing is a fundamental biological process.
• The spliceosome, a large ribonucleoprotein machinery, carries out pre-mRNA splicing.
• Understanding the spliceosome's structure is crucial for deciphering its function.

Purpose of the Study:

• To elucidate the atomic structure of the spliceosome.
• To understand the structural dynamics and catalytic mechanisms of pre-mRNA splicing.
• To characterize the roles of RNA and protein components in spliceosome function.

Main Methods:

• Cryo-electron microscopy (Cryo-EM) to determine high-resolution structures.
• Structural analysis of four distinct conformational states of the yeast spliceosome.
• Biochemical assays to investigate catalytic activity and metal ion coordination.

Main Results:

• Atomic structures of four yeast spliceosome conformational states were determined.
• The catalytic active site features two metal ions coordinated by U6 small nuclear RNA (snRNA).
• Specific RNA elements (U5, U6, and 5'-end of U2 snRNA) are rigid, stabilized by core proteins (Prp8 and 16).
• Mobile U2 snRNA sequences facilitate intron branch site delivery.
• Structural rearrangements enable exon ligation and 3'-splice site recruitment.

Conclusions:

• The spliceosome functions as a protein-directed metalloribozyme.
• Structural insights reveal the mechanism of catalysis and dynamic rearrangements during splicing.
• Prp8 and 16 proteins are key to maintaining spliceosome integrity and function.