A 10S galectin-3-U1 snRNP complex assembles into active spliceosomes

Area of Science:

• Molecular Biology
• RNA Biology
• Cell Biology

Background:

• Previous studies identified a 10S particle containing galectin-3 and U1 snRNP in HeLa cell nuclear extracts.
• This particle was shown to be capable of loading galectin-3 onto pre-mRNA substrates.

Purpose of the Study:

• To investigate the functional role of the galectin-3-U1 snRNP particle in pre-mRNA splicing.
• To determine if this complex is necessary for the formation of a productive spliceosome.

Main Methods:

• Fractionation of HeLa cell nuclear extracts using glycerol gradients.
• Immunoprecipitation using anti-galectin-3 antibodies to isolate specific protein complexes.
• Assessing splicing activity in U1 snRNP-depleted extracts and reconstituted systems.

Main Results:

• The galectin-3-U1 snRNP particle forms a productive spliceosomal complex with pre-mRNA, leading to splicing intermediates and products.
• Depletion of U1 snRNP abolished splicing activity, which could be restored by the purified galectin-3-U1 snRNP particle.
• Free galectin-3, lacking U1 snRNP, did not restore splicing activity, indicating the complex's necessity.

Conclusions:

• The galectin-3-U1 snRNP-pre-mRNA ternary complex represents a functional E complex in spliceosome assembly.
• U1 snRNP is critical for the proper assembly of galectin-3 onto an active spliceosome.