biostudies-literatureMestre-Fos SHHS | National Institutes of HealthNIEHS NIH HHSNational Aeronautics and Space AdministrationIntramural NASANational Science Foundation14855-14865https://www.ebi.ac.uk/biostudies/studies/S-EPMC7606673biostudies-literatureUnknown295(44)The <i>in vitro</i> formation of stable G-quadruplexes (G4s) in human rRNA was recently reported. However, their formation in cells and their cellular roles were not resolved. Here, by taking a chemical biology approach that integrates results from immunofluorescence, G4 ligands, heme-affinity reagents, and a genetically encoded fluorescent heme sensor, we report that human ribosomes can form G4s <i>in vivo</i> that regulate heme bioavailability. Immunofluorescence experiments indicate that the vast majority of extra-nuclear G4s are associated with rRNA. Moreover, titrating human cells with a G4 ligand alters the ability of ribosomes to bind heme and disrupts cellular heme bioavailability as measured by a genetically encoded fluorescent heme sensor. Overall, these results suggest that riboThe Journal of biological chemistryHuman ribosomal G-quadruplexes regulate heme bioavailability.PMC760667380NSSC18K1139ES025661R33 ES025661MCB-1552791R21 ES02566180NSSC17K0295Reddi ARMestre-Fos SMoore CMWilliams LDIto CfalseHuman ribosomal G-quadruplexes regulate heme bioavailability.The <i>in vitro</i> formation of stable G-quadruplexes (G4s) in human rRNA was recently reported. However, their formation in cells and their cellular roles were not resolved. Here, by taking a chemical biology approach that integrates results from immunofluorescence, G4 ligands, heme-affinity reagents, and a genetically encoded fluorescent heme sensor, we report that human ribosomes can form G4s <i>in vivo</i> that regulate heme bioavailability. Immunofluorescence experiments indicate that the vast majority of extra-nuclear G4s are associated with rRNA. Moreover, titrating human cells with a G4 ligand alters the ability of ribosomes to bind heme and disrupts cellular heme bioavailability as measured by a genetically encoded fluorescent heme sensor. Overall, these results suggest that ribo2020-01-01T00:00:00Z2020 Oct2025-04-04T09:38:42.112Z2025-04-04T09:38:42.112ZS-EPMC76066733281734310.1074/jbc.RA120.01433210.1074/jbc.ra120.014332