title: Signal-sequence recognition by an Escherichia coli ribonucleoprotein complex.
abstract: Hydrophobic signal-sequences direct the transfer of secretory proteins across the inner membrane of prokaryotes and the endoplasmic reticulum membranes of eukaryotes. In mammalian cells, signal-sequences are recognized by the 54K protein (M(r) 54,000) of the signal recognition particle (SRP) which is believed to hold the nascent chain in a translocation-competent conformation until it contacts the endoplasmic reticulum membrane. The SRP consists of a 7S RNA and six different polypeptides. The 7S RNA and the 54K signal-sequence-binding protein (SRP54) of mammalian SRP exhibit strong sequence similarity to the 4.5S RNA and P48 protein (Ffh) of Escherichia coli which form a ribonucleoprotein particle. Depletion of 4.5S RNA or overproduction of P48 causes the accumulation of the beta-lactamase precursor, although not of other secretory proteins. Whether 4.5S RNA and P48 are part of an SRP-like complex with a role in protein export is controversial. Here we show that the P48/4.5S RNA ribonucleoprotein complex interacts specifically with the signal sequence of a nascent secretory protein and therefore is a signal recognition particle.
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D003432:Cross-Linking Reagents; D004926:Escherichia coli / Q000378:metabolism; D046911:Macromolecular Substances; D011498:Protein Precursors / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000378:metabolism*; D012329:RNA, Bacterial / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism*; D018271:Signal Recognition Particle
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D046911:Macromolecular Substances; D011498:Protein Precursors; D021382:Protein Sorting Signals; D012329:RNA, Bacterial; D012261:Ribonucleoproteins; D018271:Signal Recognition Particle