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Matrin CYP, an SR-rich cyclophilin that associates with the nuclear matrix and splicing factors
1Department of Biological Sciences, State University of New York, Buffalo, New York 14260, USA.
Abstract:
We report the identification and cloning of a nuclear matrix protein termed matrin cyclophilin or matrin CYP. The derived sequence of matrin cyp encodes a protein of 752 amino acids with a predicted mass of 88 kDa. A 172-residue stretch at the amino terminus shows high identity with the ubiquitous family of cyclophilins. Clustered throughout the carboxyl half of the protein are a series of serine-arginine (SR) repeats that are a characteristic feature of many RNA splicing factors. Antibodies raised against matrin CYP recognize a 106-kDa antigen that is detected in isolated nuclei and quantitatively subfractionates in the nuclear matrix. Laser scanning confocal microscopy localizes most of the anti-matrin CYP-specific antigen within the nucleus in a pattern of large bright speckles that co-localize with splicing factors and diffuse nucleoplasmic staining. A strikingly similar pattern of staining is observed in cells extracted for in situ nuclear matrices. A fusion protein containing the cyclophilin domain of matrin CYP exhibits cyclosporin A (CsA)-sensitive, peptidylprolyl cis-trans-isomerase activity that is characteristic of native cyclophilins. Although total rat liver nuclei contains predominantly CsA-resistant PPIase activity, the corresponding activity in the nuclear matrix is largely CsA-sensitive.
Insights
Researchers identified a novel nuclear matrix protein, matrin cyclophilin (matrin CYP), with cyclophilin and RNA splicing factor domains. This protein exhibits peptidylprolyl cis-trans-isomerase activity, primarily within the nuclear matrix.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The nuclear matrix is a dynamic structure involved in nuclear organization and function.
- Proteins within the nuclear matrix play crucial roles in processes like DNA replication, transcription, and RNA processing.
Purpose of the Study:
- To identify and characterize novel proteins associated with the nuclear matrix.
- To investigate the functional properties of a newly discovered nuclear matrix protein, matrin cyclophilin (matrin CYP).
Main Methods:
- Protein identification and cloning
- Antibody generation and western blotting
- Laser scanning confocal microscopy
- Enzyme activity assays (peptidylprolyl cis-trans-isomerase)
Main Results:
- Identification of matrin cyclophilin (matrin CYP), a 752-amino acid protein with cyclophilin and serine-arginine (SR) repeat domains.
- Matrin CYP localizes to the nucleus in distinct speckles, co-localizing with splicing factors within the nuclear matrix.
- The cyclophilin domain of matrin CYP exhibits cyclosporin A-sensitive peptidylprolyl cis-trans-isomerase activity, predominantly found in the nuclear matrix.
Conclusions:
- Matrin cyclophilin is a novel nuclear matrix protein with enzymatic activity and structural features suggesting roles in RNA splicing and nuclear organization.
- The localization and enzymatic properties of matrin CYP highlight its functional significance within the nuclear matrix.