title: The structure of Escherichia coli signal recognition particle revealed by scanning transmission electron microscopy.
abstract: Structural studies on various domains of the ribonucleoprotein signal recognition particle (SRP) have not converged on a single complete structure of bacterial SRP consistent with the biochemistry of the particle. We obtained a three-dimensional structure for Escherichia coli SRP by cryoscanning transmission electron microscopy and mapped the internal RNA by electron spectroscopic imaging. Crystallographic data were fit into the SRP reconstruction, and although the resulting model differed from previous models, they could be rationalized by movement through an interdomain linker of Ffh, the protein component of SRP. Fluorescence resonance energy transfer experiments determined interdomain distances that were consistent with our model of SRP. Docking our model onto the bacterial ribosome suggests a mechanism for signal recognition involving interdomain movement of Ffh into and out of the nascent chain exit site and suggests how SRP could interact and/or compete with the ribosome-bound chaperone, trigger factor, for a nascent chain during translation.
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton L8N 3Z5, Canada.
authors.forename: Iain L
authors.initials: IL
authors.lastname: Mainprize
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Beniac
authors.forename: Elena
authors.initials: E
authors.lastname: Falkovskaia
authors.forename: Robert M
authors.initials: RM
authors.lastname: Cleverley
authors.forename: Lila M
authors.initials: LM
authors.lastname: Gierasch
authors.forename: F Peter
authors.initials: FP
authors.lastname: Ottensmeyer
authors.forename: David W
authors.initials: DW
authors.lastname: Andrews
mesh_terms: D004926:Escherichia coli / Q000648:ultrastructure*; D031541:Fluorescence Resonance Energy Transfer; D017348:Microscopy, Electron, Scanning Transmission / Q000379:methods*; D046032:Microscopy, Energy-Filtering Transmission Electron; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D012329:RNA, Bacterial / Q000737:chemistry; D012270:Ribosomes / Q000378:metabolism; D018271:Signal Recognition Particle / Q000648:ultrastructure*; D012996:Solutions
chemical_list: D021122:Protein Subunits; D012329:RNA, Bacterial; D018271:Signal Recognition Particle; D012996:Solutions