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Cytoplasmic dynein contains a family of differentially expressed light chains
S M King1, E Barbarese, J F Dillman
1Department of Biochemistry, Center for Biomedical Imaging Technology, University of Connecticut Health Center, Farmington 06032-3305, USA. king@panda.uch.edu
Abstract:
Cytoplasmic dynein contains a series of accessory proteins associated with the motor containing heavy chains.1 These include three distinct classes of light chains (Mr < approximately 22 000). Here we demonstrate that a previously cloned protein termed rp3 is a bona fide Mr 14 000 light chain component of this microtubule motor complex. The rp3 polypeptide is approximately 55% identical to the Tctex1 dynein light chain, and together, these two proteins define one branch of a diverse family of Mr 14 000 light chains associated with both cytoplasmic and flagellar dyneins. The Tctex1 and rp3 light chains are differentially expressed in various tissues: rp3 is most prevalent in liver and brain cytoplasmic dynein, whereas those tissues contain the least amounts of Tctex1. Immunofluorescence analysis was consistent with the tissue-specific distribution of these proteins and revealed that both rp3 and Tctex1 are present in multiple perinuclear punctate particles. Furthermore, in two cell lines, rp3 was found associated with an elongated structure located in the layer of cytoplasm above the nucleus. Electrophoretic/immunological analysis indicates that there are only single isoforms for these proteins in brain and PC-12 cells, suggesting that alterations in the Mr 14 000 light chains of dynein are achieved at the level of the individual proteins and not by posttranslational modification. Dissection of the cytoplasmic dynein complex revealed that Tctex1, an Mr 8000 LC dimer, and IC74 associate to define a basal-located intermediate chain/light chain complex analogous to that found in flagellar outer arm dynein.
Insights
A newly identified rp3 protein is a Mr 14,000 light chain in cytoplasmic dynein. This protein, along with Tctex1, forms a diverse family of light chains found in microtubule motor complexes.
Area of Science:
- Cell Biology
- Molecular Motors
- Protein Biochemistry
Background:
- Cytoplasmic dynein is a crucial microtubule motor complex.
- This motor comprises heavy chains and various accessory proteins, including distinct classes of light chains (Mr < 22,000).
Purpose of the Study:
- To identify and characterize a previously cloned protein, rp3, as a component of the cytoplasmic dynein motor.
- To investigate the relationship between rp3 and other dynein light chains, such as Tctex1.
- To explore the tissue-specific expression and localization of rp3 and Tctex1.
Main Methods:
- Protein cloning and characterization.
- Sequence homology analysis to compare rp3 with known dynein light chains.
- Tissue-specific expression analysis using electrophoretic and immunological methods.
- Immunofluorescence microscopy to determine subcellular localization.
Main Results:
- rp3 was confirmed as a Mr 14,000 light chain component of cytoplasmic dynein.
- rp3 shares approximately 55% identity with Tctex1, defining a family of Mr 14,000 light chains.
- rp3 and Tctex1 exhibit differential tissue expression, with rp3 abundant in liver and brain.
- Both proteins localize to perinuclear punctate particles and specific cellular structures.
- Analysis suggests alterations in light chains occur at the protein level, not via posttranslational modification.
Conclusions:
- rp3 is a novel Mr 14,000 dynein light chain with distinct tissue distribution.
- The rp3 and Tctex1 proteins represent a significant branch of the dynein light chain family.
- Dynein light chain composition is regulated at the individual protein level, impacting motor function.