The Drosophila hnRNP F/H Homolog Glorund Uses Two Distinct RNA-Binding Modes to Diversify Target Recognition

Abstract

Summary The Drosophila hnRNP F/H homolog, Glorund (Glo), regulates nanos mRNA translation by interacting with a structured UA-rich motif in the nanos 3′ untranslated region. Glo regulates additional RNAs however, and mammalian homologs bind G-tract sequences to regulate alternative splicing, suggesting that Glo also recognizes G-tract RNA. To gain insight into how Glo recognizes both structured UA-rich and G-tract RNAs, we used mutational analysis guided by crystal structures of Glo’s RNA-binding domains and identified two discrete RNA-binding surfaces that allow Glo to recognize both RNA motifs. By engineering Glo variants that favor a single RNA-binding mode, we show that a subset of Glo’s functions in vivo is mediated solely by the G-tract binding mode, whereas regulation of nanos requires both recognition modes. Our findings suggest a molecular mechanism for the evolution of dual RNA motif recognition in Glo that may be applied to understanding the functional diversity of other RNA-binding proteins.

Structural Insight into DNA-Dependent Activation of Human Metalloprotease Spartan

“…A Dali server search with the structure of the ZBD as the query did not return significant hits that matched known ZBDs or motifs, suggesting that the ZBD represents a unique Zn 2+ -binding fold. The closest match to the ZBD was the quasi-RNA-recognition motifs (qRRMs) of the Drosophila protein Glorund, which do not bind to Zn 2+ (PDB: 5UZN) (Tamayo et al, 2017). Thus, the ZBD is a Zn 2+ and nucleic acid-binding domain.…”

SAM68 is required for regulation of Pumilio by the NORAD long noncoding RNA

“…7B). The binding location of HNRNPF within NRUs is currently less clear, as HNRNPF was reported to bind U/G-rich sequences (Huelga et al 2012) or GGG motifs (Van Nostrand et al 2017), but its fly homolog, Glorund, recognizes both GGG and structured A/U-rich elements (Tamayo et al 2017). Since SAM68 and HNRNPF binding in the MS data was affected by the mutations in multiple structured elements, an interesting possibility is that the conserved hairpin elements in the NRUs are conserved not because they serve as binding sites for a particular protein but rather because they help position the protein-binding sites at a favorable distance and orientation from each other.…”

Translational Control during Developmental Transitions

“…Regardless of such differences, translation of germ plasm-enriched mRNAs is also tightly regulated, with most of them being repressed during oogenesis and individually activated during embryogenesis (Rangan et al 2009). For instance, nos mRNA translation is repressed during oogenesis by Glorund and Smaug (Smg), two RNA-binding proteins that interact with the nos 3 0 UTR (Smibert et al 1999;Kalifa et al 2006;Tamayo et al 2017). Similarly to Bru, Smg interacts with Cup, which then binds to eIF4E and inhibits nos translation initiation by precluding the eIF4E-eIF4G interaction and formation of the preinitiation complex at the 5 0 end of nos mRNA (Nelson et al 2004;Andrews et al 2011).…”