A crystal structure of a collaborative RNA regulatory complex reveals mechanisms to refine target specificity

Elife. 2019 Aug 9;8:e48968. doi: 10.7554/eLife.48968.


In the Caenorhabditis elegans germline, fem-3 Binding Factor (FBF) partners with LST-1 to maintain stem cells. A crystal structure of an FBF-2/LST-1/RNA complex revealed that FBF-2 recognizes a short RNA motif different from the characteristic 9-nt FBF binding element, and compact motif recognition coincided with curvature changes in the FBF-2 scaffold. Previously, we engineered FBF-2 to favor recognition of shorter RNA motifs without curvature change (Bhat et al., 2019). In vitro selection of RNAs bound by FBF-2 suggested sequence specificity in the central region of the compact element. This bias, reflected in the crystal structure, was validated in RNA-binding assays. FBF-2 has the intrinsic ability to bind to this shorter motif. LST-1 weakens FBF-2 binding affinity for short and long motifs, which may increase target selectivity. Our findings highlight the role of FBF scaffold flexibility in RNA recognition and suggest a new mechanism by which protein partners refine target site selection.

Keywords: C. elegans; PUF protein; RNA; RNA-binding protein; X-ray crystallography; developmental biology; molecular biophysics; structural biology.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Caenorhabditis elegans / chemistry*
  • Caenorhabditis elegans / metabolism*
  • Caenorhabditis elegans Proteins / chemistry
  • Caenorhabditis elegans Proteins / metabolism*
  • Crystallography, X-Ray
  • Protein Binding
  • RNA / chemistry
  • RNA / metabolism*
  • RNA-Binding Proteins / chemistry
  • RNA-Binding Proteins / metabolism*


  • Caenorhabditis elegans Proteins
  • LST-1 protein, C elegans
  • RNA-Binding Proteins
  • fem-3-binding protein, C elegans
  • RNA

Associated data

  • Dryad/10.5061/dryad.30501q7
  • PDB/6PUN