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The Ct-RAE1 protein interacts with Balbiani ring RNP particles at the nuclear pore
Abstract:
RAE1 is an evolutionarily conserved protein that associates with both mRNPs and nucleoporins, and may bridge the interaction between mRNP export cargoes and the nuclear pore complex (NPC). However, the mechanism by which RAE1 functions in mRNA export is still unknown and the time point at which RAE1 interacts with the exported RNP has not been directly investigated. Here we have addressed this question in the Balbiani ring (BR) system of Chironomus tentans using immunoelectron microscopy. The RAE1 protein of C. tentans, Ct-RAE1, is 70% identical to human RAE1/mrnp41 (hRAE1) and is recognized by antibodies raised against hRAE1. As in vertebrate cells, Ct-RAE1 is concentrated at the nuclear envelope and also dispersed throughout the nuclear interior. Here we show that Ct-RAE1 does not bind to the BR particle either cotranscriptionally or in the nucleoplasm. Instead, the interaction between Ct-RAE1 and the exported BR particle occurs at the NPC. Moreover, the localization of Ct-RAE1 at the NPC is correlated with the presence of an exported RNP in the NPC. Finally, the anti-RAE1 antibody does not label the cytoplasmic side of BR particles in transit through the central channel, which indicates that Ct-RAE1 either remains anchored at the nuclear side of the NPC during translocation of the RNP through the central channel or becomes transiently associated with the RNP but is rapidly released into the cytoplasm.
Insights
RAE1 protein interacts with messenger ribonucleoprotein (mRNP) particles at the nuclear pore complex (NPC), not during transcription or in the nucleoplasm. This interaction is crucial for mRNA export, with RAE1 likely remaining at the nuclear side of the NPC.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- RAE1 protein is involved in mRNA export, associating with mRNPs and nucleoporins.
- The precise mechanism and timing of RAE1's interaction with mRNA export cargoes remain unclear.
Purpose of the Study:
- To investigate the temporal interaction of RAE1 with exported messenger ribonucleoprotein (mRNP) particles.
- To elucidate the role of RAE1 in mRNA export using the Balbiani ring (BR) system in Chironomus tentans.
Main Methods:
- Immunoelectron microscopy was employed in the Balbiani ring (BR) system of Chironomus tentans.
- Antibodies against human RAE1 (hRAE1) were used to detect the C. tentans RAE1 (Ct-RAE1) protein.
Main Results:
- Ct-RAE1 interacts with BR particles specifically at the nuclear pore complex (NPC), not during transcription or in the nucleoplasm.
- Ct-RAE1 localization at the NPC correlates with the presence of exported RNP particles within the NPC.
- RAE1 does not appear on the cytoplasmic side of BR particles passing through the NPC's central channel.
Conclusions:
- RAE1's function in mRNA export involves interaction at the NPC, rather than earlier stages of mRNP biogenesis.
- Ct-RAE1 likely remains anchored to the nuclear side of the NPC or is transiently associated during RNP translocation.