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SR proteins: a conserved family of pre-mRNA splicing factors
A M Zahler1, W S Lane, J A Stolk
1Fred Hutchinson Cancer Research Center, Division of Basic Sciences, Seattle, Washington 98104.
Abstract:
We demonstrate that four different proteins from calf thymus are able to restore splicing in the same splicing-deficient extract using several different pre-mRNA substrates. These proteins are members of a conserved family of proteins recognized by a monoclonal antibody that binds to active sites of RNA polymerase II transcription. We purified this family of nuclear phosphoproteins to apparent homogeneity by two salt precipitations. The family, called SR proteins for their serine- and arginine-rich carboxy-terminal domains, consists of at least five different proteins with molecular masses of 20, 30, 40, 55, and 75 kD. Microsequencing revealed that they are related but not identical. In four of the family members a repeated protein sequence that encompasses an RNA recognition motif was observed. We discuss the potential role of this highly conserved, functionally related set of proteins in pre-mRNA splicing.
Insights
Four calf thymus proteins, identified as SR proteins, can restore pre-messenger RNA (pre-mRNA) splicing in deficient extracts. These conserved nuclear phosphoproteins possess RNA recognition motifs, suggesting a key role in splicing regulation.
Area of Science:
- Molecular Biology
- RNA Processing
- Protein Biochemistry
Background:
- Pre-mRNA splicing is crucial for gene expression.
- Splicing-deficient cellular extracts hinder research into splicing mechanisms.
- Conserved protein families often play fundamental roles in cellular processes.
Purpose of the Study:
- To identify and characterize proteins involved in pre-mRNA splicing.
- To investigate the function of a conserved family of nuclear phosphoproteins in splicing.
- To elucidate the structural and functional relationships within this protein family.
Main Methods:
- Purification of nuclear phosphoproteins from calf thymus using salt precipitation.
- Assay of protein activity in restoring splicing in a splicing-deficient extract.
- Microsequencing to determine protein identity and relationships.
- Analysis of protein domains, including RNA recognition motifs.
Main Results:
- Four distinct proteins from calf thymus restored splicing in a splicing-deficient extract with various pre-mRNA substrates.
- These proteins belong to a conserved family, termed SR proteins, characterized by serine- and arginine-rich domains.
- The SR protein family comprises at least five members (20, 30, 40, 55, and 75 kD).
- Microsequencing indicated relatedness among family members, with four containing an RNA recognition motif.
Conclusions:
- SR proteins are essential for pre-mRNA splicing.
- The conserved nature and RNA-binding motifs of SR proteins suggest a significant role in splicing regulation.
- Further investigation into the specific functions of these SR proteins is warranted.