Evidence for cooperative tandem binding of hnRNP C RRMs in mRNA processing

RNA. 2015 Nov;21(11):1931-42. doi: 10.1261/rna.052373.115. Epub 2015 Sep 14.


The human hnRNP C is a ubiquitous cellular protein involved in mRNA maturation. Recently, we have shown that this protein specifically recognizes uridine (U) pentamers through its single RNA recognition motif (RRM). However, a large fraction of natural RNA targets of hnRNP C consists of much longer contiguous uridine stretches. To understand how these extended sites are recognized, we studied the binding of the RRM to U-tracts of 8-11 bases. In vivo investigation of internal translation activation of unr (upstream of N-ras) mRNA indicates that the conservation of the entire hnRNP C binding site, UC(U)8, is required for hnRNP C-dependent IRES activation. The assays further suggest a synergistic interplay between hnRNP C monomers, dependent on the protein's ability to oligomerize. In vitro spectroscopic and thermodynamic analyses show that isolated RRMs bind to (U)11 oligomers as dimers. Structural modeling of a ternary double-RRM/RNA complex indicates additionally that two RRM copies can be accommodated on the canonical sequence UC(U)8. The proposed tandem RRM binding is in very good agreement with the transcriptome-wide recognition of extended U-tracts by full-length hnRNP C, which displays a cross-linking pattern consistent with a positively cooperative RRM dimer binding model.

Keywords: IRES; RRM; alternative splicing; hnRNP C; uridine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites / genetics*
  • Heterogeneous-Nuclear Ribonucleoprotein Group C / metabolism*
  • Heterogeneous-Nuclear Ribonucleoproteins / genetics
  • Humans
  • Protein Binding / genetics*
  • RNA Recognition Motif Proteins / metabolism*
  • RNA, Messenger / genetics*
  • RNA, Messenger / metabolism*
  • Transcriptome / genetics
  • Uridine / genetics
  • Uridine / metabolism


  • Heterogeneous-Nuclear Ribonucleoprotein Group C
  • Heterogeneous-Nuclear Ribonucleoproteins
  • RNA Recognition Motif Proteins
  • RNA, Messenger
  • Uridine