Abstract
During mRNA localization, RNA-binding proteins interact with specific structured mRNA localization motifs. Although several such motifs have been identified, we have limited structural information on how these interact with RNA-binding proteins. Staufen proteins bind structured mRNA motifs through dsRNA-binding domains (dsRBD) and are involved in mRNA localization in Drosophila and mammals. We solved the structure of two dsRBDs of human Staufen1 in complex with a physiological dsRNA sequence. We identified interactions between the dsRBDs and the RNA sugar-phosphate backbone and direct contacts of conserved Staufen residues to RNA bases. Mutating residues mediating nonspecific backbone interactions only affected Staufen function in Drosophila when in vitro binding was severely reduced. Conversely, residues involved in base-directed interactions were required in vivo even when they minimally affected in vitro binding. Our work revealed that Staufen can read sequence features in the minor groove of dsRNA and suggests that these influence target selection in vivo.
Highlights
The intracellular localization of mRNAs is a critical gene regulatory mechanism in many eukaryotic cell types and processes
These cis elements are bound by trans-acting factors, or RNAbinding proteins that mediate the recruitment of additional components required for transport, anchoring, and translational control of the mRNA
During the asymmetric division of embryonic neuroblasts, Drosophila Stau (dStau) associates with prospero mRNA and restricts its localization to the daughter cell, which will differentiate into a ganglion mother cell (Broadus & Doe, 1997; Li et al, 1997; Broadus et al, 1998; Fuerstenberg et al, 1998; Matsuzaki et al, 1998; Schuldt et al, 1998; Shen et al, 1998)
Summary
The intracellular localization of mRNAs is a critical gene regulatory mechanism in many eukaryotic cell types and processes (reviewed in Martin & Ephrussi [2009]; Meignin & Davis [2010]; Medioni et al [2012]; Chin & Lecuyer [2017]). A key step in the pathway is the specific recognition of the localizing transcript, which depends on linear or structured cis-acting signals, generally located in the mRNA 39UTR. These cis elements are bound by trans-acting factors, or RNAbinding proteins that mediate the recruitment of additional components required for transport, anchoring, and translational control of the mRNA. Drosophila Stau (dStau) is required for oskar (osk) mRNA transport to the posterior pole of the oocyte, where abdomen and germ cells will develop (Ephrussi et al, 1991; Kim-Ha et al, 1991, 1995, St Johnston et al, 1991, 1992). During the asymmetric division of embryonic neuroblasts, dStau associates with prospero (pros) mRNA and restricts its localization to the daughter cell, which will differentiate into a ganglion mother cell (Broadus & Doe, 1997; Li et al, 1997; Broadus et al, 1998; Fuerstenberg et al, 1998; Matsuzaki et al, 1998; Schuldt et al, 1998; Shen et al, 1998)
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