RNA Splicing Mechanisms and Regulation

Study Notes

Splicing Mechanisms and Alternative Splicing

Proteins interact with U1 and U2 snRNPs, binding to sequences near splice sites, influencing splicing.
Many sequences around splice junctions and branch points are crucial for proper splicing.
These sequences are separate from splice sites themselves but determine splicing efficiency.

RNA-Binding Proteins and Splicing Regulation

RNA-binding proteins recognize short motifs near splice sites.
Some proteins promote splicing, while others inhibit it.
Exonic splicing enhancers (ESEs) are found within exons.
They facilitate splicing at nearby splice junctions.
SR proteins bind to ESEs, labeling exons for splicing.
SR proteins have RNA-binding domains and protein-protein interaction domains.
They interact directly with U1 snRNP and indirectly with U2 snRNP.
- Interaction with U2 snRNP is facilitated by factors nearby the 3' splice site.

U2 snRNP and 3' Splice Site Interactions

U2 snRNP binds to the branch point sequence.
It also recruits components that define the 3' splice site boundary.
U2AF65 binds to a polypyrimidine tract near the 3' splice site.
U2AF35 binds directly to the 3' splice site.
Interactions ensure the spliceosome recognizes the correct splice site.
SR proteins assist this process by marking exons.

Alternative Splicing Definition

In alternative splicing, a single pre-mRNA can be spliced into multiple mRNA variants.
This creates various protein isoforms from a single gene.

Alternative Splicing Examples and Impact

Fibronectin gene: Different isoforms exist. Fibroblasts create a 'sticky' form of fibronectin, while hepatocytes create a form that doesn't interact with the extracellular matrix.
Calcium-activated potassium channels in the ear: Multiple variations of this gene product exist. Different isoforms respond to specific calcium concentrations, facilitating sound detection at varied frequencies.

Alternative Splicing Benefits and Key Points

Offers a significant increase in the total number of proteins a genome can produce.
It allows gene expression to be tuned to specific cell types.
In some cases, very high levels of alternative splicing exist, exemplified by the multiple isoforms of calcium-activated potassium channels in the ear.
SR proteins interact with the spliceosome machinery to mark exons for proper splicing.

Description

Explore the intricate mechanisms of RNA splicing, focusing on splicing factors like U1 and U2 snRNPs, as well as the role of RNA-binding proteins. This quiz will test your understanding of how specific sequences influence splicing efficiency and the regulatory roles of exonic splicing enhancers. Delve into the complexities of splicing regulation and the critical interactions that ensure proper protein synthesis.