Related Experiment Videos
Phosphorylation of spliceosomal protein SAP 155 coupled with splicing catalysis
1Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.pende014@mc.duke.edu
Abstract:
The U2 snRNP component SAP 155 contacts pre-mRNA on both sides of the branch site early in spliceosome assembly and is therefore positioned near or at the spliceosome catalytic center. We have isolated a cDNA encoding human SAP 155 and identified its highly related Saccharomyces cerevisiae homolog (50% identity). The carboxy-terminal two-thirds of SAP 155 shows the highest conservation and is remarkably similar to the regulatory subunit A of the phosphatase PP2A. Significantly, SAP 155 is phosphorylated concomitant with or just after catalytic step one, making this the first example of a protein modification tightly regulated with splicing catalysis.
Insights
Researchers identified the human SAP 155 protein, crucial for spliceosome assembly. This protein is phosphorylated during splicing catalysis, revealing a novel regulatory mechanism in gene expression.
Area of Science:
- Molecular Biology
- RNA Splicing
- Protein Phosphorylation
Background:
- The spliceosome is a complex molecular machine responsible for RNA splicing.
- SAP 155 is a component of the U2 small nuclear ribonucleoprotein particle (snRNP).
- SAP 155's position suggests a role in spliceosome catalysis.
Purpose of the Study:
- To isolate the cDNA encoding human SAP 155.
- To identify homologous proteins in other organisms.
- To investigate the phosphorylation status of SAP 155 during splicing.
Main Methods:
- cDNA isolation and sequencing.
- Homology searches using bioinformatics tools.
- Analysis of protein phosphorylation during in vitro splicing assays.
Main Results:
- Human SAP 155 cDNA was isolated and characterized.
- A highly conserved homolog of SAP 155 was identified in Saccharomyces cerevisiae.
- SAP 155 undergoes phosphorylation during or immediately after the first catalytic step of splicing.
Conclusions:
- SAP 155 is a conserved splicing factor with a potential link to protein phosphatase 2A (PP2A).
- The phosphorylation of SAP 155 is tightly regulated by splicing catalysis.
- This represents the first identified instance of protein modification linked to spliceosome catalytic activity.