U2 spliceosomal RNA

U2 spliceosomal RNA (snRNA) is a key component of the major spliceosome, responsible for recognizing branch site sequences in pre-mRNA during splicing. It forms part of the U2 snRNP complex, which plays a crucial role in spliceosome assembly and catalysis. U2 interacts with other snRNAs, such as U6, to form a conserved secondary structure that resembles domain V of group II introns, suggesting an evolutionary link between spliceosomes and self-splicing introns.

The U2 snRNA contains several conserved regions important for function, including the branch site-binding region (BSR) and the 5' cap. Modifications such as pseudouridylation, methylation, and trimethylation of the guanosine cap are critical for its stability and activity. These modifications influence spliceosomal dynamics and accuracy.

During splicing, U2 undergoes conformational changes that facilitate interactions with other snRNAs and proteins. The U2-U6 folding event creates a four-helix junction that scaffolds the active site, aligning the branch point adenosine for attack by the 5' splice site hydroxyl group.

The structural similarity between U2-U6 and group II introns highlights their shared evolutionary origin. Both systems employ a two-metal-ion mechanism for catalysis, emphasizing their common ancestry in RNA-based splicing machinery. This relationship underscores the deep conservation of RNA folding and catalytic mechanisms across evolution.