title: Escherichia coli rimM and yjeQ null strains accumulate immature 30S subunits of similar structure and protein complement.
abstract: Assembly of the Escherichia coli 30S ribosomal subunits proceeds through multiple parallel pathways. The protein factors RimM, YjeQ, RbfA, and Era work in conjunction to assist at the late stages of the maturation process of the small subunit. However, it is unclear how the functional interplay between these factors occurs in the context of multiple parallel pathways. To understand how these factors work together, we have characterized the immature 30S subunits that accumulate in ΔrimM cells and compared them with immature 30S subunits from a ΔyjeQ strain. The cryo-EM maps obtained from these particles showed that the densities representing helices 44 and 45 in the rRNA were partially missing, suggesting mobility of these motifs. These 30S subunits were also partially depleted in all tertiary ribosomal proteins, particularly those binding in the head domain. Using image classification, we identified four subpopulations of ΔrimM immature 30S subunits differing in the amount of missing density for helices 44 and 45, as well as the amount of density existing in these maps for the underrepresented proteins. The structural defects found in these immature subunits resembled those of the 30S subunits that accumulate in the ΔyjeQ strain. These findings are consistent with an "early convergency model" in which multiple parallel assembly pathways of the 30S subunit converge into a late assembly intermediate, as opposed to the mature state. Functionally related factors will bind to this intermediate to catalyze the last steps of maturation leading to the mature 30S subunit.
authors.affiliation: Department of Biochemistry and Biomedical Sciences, and M.G. DeGroote Institute for Infectious Diseases Research, McMaster University, Hamilton, Ontario, L8N3Z5, Canada.
authors.forename: Vivian
authors.initials: V
authors.lastname: Leong
authors.forename: Meredith
authors.initials: M
authors.lastname: Kent
authors.forename: Ahmad
authors.initials: A
authors.lastname: Jomaa
authors.forename: Joaquin
authors.initials: J
authors.lastname: Ortega
mesh_terms: D001665:Binding Sites; D020285:Cryoelectron Microscopy; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D005798:Genes, Bacterial; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D010641:Phenotype; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism*; D012336:RNA, Ribosomal, 16S / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism*; D054680:Ribosome Subunits, Small, Bacterial / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D016601:RNA-Binding Proteins; C092748:RbfA protein, E coli; D012269:Ribosomal Proteins; C436973:RimM protein, E coli; C068027:era protein, E coli; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; C467318:RsgA protein, E coli
keywords: 30S subunit; RimM protein; YjeQ protein; cryo-electron microscopy; ribosome assembly