Xenbase Image ID: 116788

Figure 5. Major pathways involving DDX6-like helicases in the metabolism of mRNA of different organisms. Different aspects of helicase activity are emphasized in different organisms. In S.cerevisiae, best studied is the decay pathway in which Dhh1p has been shown to associate both with the mRNA deadenylation complex containing Ccr4p and Pop2p and the mRNA decapping complex containing Dcp1/2p, Pat1p and Lsm1-7p. Decapping activity is located in P-bodies. Deletion of DHH1 results in a block in meiosis. In Caenorhabditis, CGH-1 locates to cytoplasmic mRNP particles and to P granules. Whereas CGH-1 particles are dynamic structures responsive to meiotic development, P granules may represent sites of mRNP assembly or remodelling. CEY2-4 are CSD proteins associated with mRNA. Deletion of CGH-1 results in physiological germ cell apoptosis. In Drosophila, Me31B binds to maternal mRNAs synthesized in nurse cells. Including the CSD protein Yps and the mRNA-localization factor Exu, mRNP is exported to the oocyte where localization between anterior (A) and posterior (P) regions may occur. In addition, Me31B locates to sponge bodies, which may represent the site of germplasm. Deletion of ME31B results in premature translation of mRNAs, normally located to and stored in the oocyte, in nurse cells. In Xenopus, Xp54 can shuttle between cytoplasm and nucleus (GV) but, after binding to nascent pre-mRNA transcripts together with the CSD protein FRGY2, exits the nucleus in mRNP particles, most of these being stored in a non-translating (maternal) form. In early oocytes, Xp54 also locates to the Balbiani body that contains the germplasm. In mammalian cells, rck/p54 is bound to mRNA together with the CSD protein YB1/p50. Some mRNP may be held in a non-translating form. rck/p54 is also a component of SGs and is implicated in the remodelling of mRNP for translation, storage or degradation in P-bodies. mRNP marked for degradation is associated with the decapping enzymes Dcp1/2 and the mRNA may be eventually degraded by the 5′ exonuclease Xrn1. For references see text. 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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