Structure of Gcn1 bound to stalled and colliding 80S ribosomes

Proc Natl Acad Sci U S A. 2021 Apr 6;118(14):e2022756118. doi: 10.1073/pnas.2022756118.


The Gcn pathway is conserved in all eukaryotes, including mammals such as humans, where it is a crucial part of the integrated stress response (ISR). Gcn1 serves as an essential effector protein for the kinase Gcn2, which in turn is activated by stalled ribosomes, leading to phosphorylation of eIF2 and a subsequent global repression of translation. The fine-tuning of this adaptive response is performed by the Rbg2/Gir2 complex, a negative regulator of Gcn2. Despite the wealth of available biochemical data, information on structures of Gcn proteins on the ribosome has remained elusive. Here we present a cryo-electron microscopy structure of the yeast Gcn1 protein in complex with stalled and colliding 80S ribosomes. Gcn1 interacts with both 80S ribosomes within the disome, such that the Gcn1 HEAT repeats span from the P-stalk region on the colliding ribosome to the P-stalk and the A-site region of the lead ribosome. The lead ribosome is stalled in a nonrotated state with peptidyl-tRNA in the A-site, uncharged tRNA in the P-site, eIF5A in the E-site, and Rbg2/Gir2 in the A-site factor binding region. By contrast, the colliding ribosome adopts a rotated state with peptidyl-tRNA in a hybrid A/P-site, uncharged-tRNA in the P/E-site, and Mbf1 bound adjacent to the mRNA entry channel on the 40S subunit. Collectively, our findings reveal the interaction mode of the Gcn2-activating protein Gcn1 with colliding ribosomes and provide insight into the regulation of Gcn2 activation. The binding of Gcn1 to a disome has important implications not only for the Gcn2-activated ISR, but also for the general ribosome-associated quality control pathways.

Keywords: Gcn1; disome; ribosome; stress; translation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Carrier Proteins / metabolism
  • Molecular Dynamics Simulation
  • Peptide Elongation Factors / chemistry*
  • Peptide Elongation Factors / genetics
  • Peptide Elongation Factors / metabolism
  • Protein Binding
  • Protein Serine-Threonine Kinases / metabolism
  • RNA, Transfer, Amino Acyl / metabolism
  • Ribosomes / chemistry
  • Ribosomes / metabolism*
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins / chemistry*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism
  • Stress, Physiological


  • Carrier Proteins
  • GCN1 protein, S cerevisiae
  • Gir2 protein, S cerevisiae
  • Peptide Elongation Factors
  • RNA, Transfer, Amino Acyl
  • Rbg1 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • tRNA, peptidyl-
  • GCN2 protein, S cerevisiae
  • Protein Serine-Threonine Kinases