title: Essential ribosome assembly factor Fap7 regulates a hierarchy of RNA-protein interactions during small ribosomal subunit biogenesis.
abstract: Factor activating Pos9 (Fap7) is an essential ribosome biogenesis factor important for the assembly of the small ribosomal subunit with an uncommon dual ATPase and adenylate kinase activity. Depletion of Fap7 or mutations in its ATPase motifs lead to defects in small ribosomal subunit rRNA maturation, the absence of ribosomal protein Rps14 from the assembled subunit, and retention of the nascent small subunit in a quality control complex with the large ribosomal subunit. The molecular basis for the role of Fap7 in ribosome biogenesis is, however, not yet understood. Here we show that Fap7 regulates multiple interactions between the precursor rRNA, ribosomal proteins, and ribosome assembly factors in a hierarchical manner. Fap7 binds to Rps14 with a very high affinity. Fap7 binding blocks both rRNA-binding elements of Rps14, suggesting that Fap7 inhibits premature interactions of Rps14 with RNA. The Fap7/Rps14 interaction is modulated by nucleotide binding to Fap7. Rps14 strongly activates the ATPase activity but not the adenylate kinase activity of Fap7, identifying Rps14 as an example of a ribosomal protein functioning as an ATPase-activating factor. In addition, Fap7 inhibits the RNA cleavage activity of Nob1, the endonuclease responsible for the final maturation step of the small subunit rRNA, in a nucleotide independent manner. Thus, Fap7 may regulate small subunit biogenesis at multiple stages.
authors.affiliation: Institute of Molecular Biosciences, Institute of Biophysical Chemistry, Center for Biomolecular Magnetic Resonance, and Cluster of Excellence "Macromolecular Complexes," Johann-Wolfgang-Goethe-Universität, 60438 Frankfurt am Main, Germany.
authors.forename: Ute A
authors.initials: UA
authors.lastname: Hellmich
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Weis
authors.forename: Anatoli
authors.initials: A
authors.lastname: Lioutikov
authors.forename: Jan Philip
authors.initials: JP
authors.lastname: Wurm
authors.forename: Marco
authors.initials: M
authors.lastname: Kaiser
authors.forename: Nina A
authors.initials: NA
authors.lastname: Christ
authors.forename: Katharina
authors.initials: K
authors.lastname: Hantke
authors.forename: Peter
authors.initials: P
authors.lastname: Kötter
authors.forename: Karl-Dieter
authors.initials: KD
authors.lastname: Entian
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
authors.forename: Jens
authors.initials: J
authors.lastname: Wöhnert
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000263:Adenylate Kinase / Q000378:metabolism*; D000595:Amino Acid Sequence; D001703:Biophysics; D002850:Chromatography, Gel; D002855:Chromatography, Thin Layer; D002942:Circular Dichroism; D005454:Fluorescence Polarization; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D043902:Pyrococcus horikoshii / Q000201:enzymology*; D012269:Ribosomal Proteins / Q000378:metabolism*; D054679:Ribosome Subunits, Small / Q000502:physiology*; D016415:Sequence Alignment; D013045:Species Specificity; D013050:Spectrometry, Fluorescence; D020798:Two-Hybrid System Techniques
chemical_list: D012269:Ribosomal Proteins; D000263:Adenylate Kinase; D000251:Adenosine Triphosphatases