RNA-associated protein 55 (RAP55) localizes to mRNA processing bodies and stress granules
- 1Departments of Medicine, Anesthesia, and Critical Care, and The Center for Immunology and Inflammatory Diseases, 2The Diabetes Research Laboratory, and 3The Cardiovascular Research Center of the General Medical Services, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
Abstract
The mRNA processing body (P-body) is a cellular structure that has an important role in mRNA degradation. P-bodies have also been implicated in RNAi-mediated post-transcriptional gene silencing. The objective of this study was to identify and characterize novel components of the mammalian P-body. Approximately 5% of patients with the autoimmune disease primary biliary cirrhosis have antibodies directed against this structure. Serum from one of these patients was used to identify a cDNA encoding RAP55, a 463–amino acid protein. RAP55 colocalized with previously identified P-body components DCP1a and Ge-1. RAP55 contains an N-terminal Sm-like domain and two C-terminal RGG-rich domains separated by an FDF motif. The two RGG domains and the FDF domain were necessary and sufficient to target the protein to P-bodies. A fragment of RAP55 consisting of the FDF and the second RGG domains did not localize to P-bodies, but was able to displace other P-body components from this structure. After cells were subjected to arsenite-induced stress, RAP55 was detected in TIA-containing stress granules. The second RGG domain was necessary and sufficient for stress granule localization. siRNA-mediated knock-down of RAP55 resulted in loss of P-bodies, suggesting that RAP55 acts prior to the 5′-decapping step in mRNA degradation. The results of this study show that RAP55 is a component of P-bodies in cells at rest and localizes in stress granules in arsenite-treated cells. RAP55 may serve to shuttle mRNAs between P-bodies and stress granules.
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Footnotes
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↵4 These authors contributed equally to this work.
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Article published online ahead of print. Article and publication date are at http://www.rnajournal.org/cgi/doi/10.1261/rna.2302706.
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- Accepted January 3, 2006.
- Received November 27, 2005.
- Copyright 2006 by RNA Society
