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Figure 3. Diagram indicating possible interactions of mRNA-bound and associated proteins involved with Xp54 helicase in the remodelling of mRNP for storage, translation and degradation. FRGY2 is the major mRNA masking protein that avidly binds single-stranded RNA. Stability of RNA binding is maintained by continuous phosphorylation (P red) of FRGY2 oligomers by CK2α, which is an integral component of stored mRNP particles. The RNA helicase Xp54 can be efficiently crosslinked to an abundant mRNP component Rap, which is an RNA-associated protein that may regulate helicase activity. Furthermore, translation repression may involve formation of a 3′–5′ molecular bridge between the protein that binds to the cytoplasmic polyadenylation element (CPEB), oligomerized Xp54 and the cap-binding protein eIF4E. The eIF4E regulatory protein 4E-T may be required to complete the bridge. In translation activation, the poly(A) tail is generally extended and most, but not all, of FRGY2 is released from the mRNA, apparently through interaction with the acidic chaperone, nucleoplasmin (51) and/or phosphorylation by the protein kinase Akt (52). In addition, the translation initiation factor eIF4G may displace the co-repressor 4E-T and form a bridge with poly(A)-binding protein bound to the extended tail (data not shown). Coincident with translation activation is phosphorylation of Xp54 (P red) by an unidentified protein kinase (PK). During mRNA degradation, studies on other systems (71) indicate that deadenylation is followed by decapping (Dcp1/2) and exonuclease digestion by Xrn1 (data not shown). Image published in: Weston A and Sommerville J (2006) © 2006 The Author(s). This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license Larger Image Printer Friendly View

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