title: A point mutation in ribosomal protein L7/L12 reduces its ability to form a compact dimer structure and to assemble into the GTPase center.
abstract: An Escherichia coli mutant, LL103, harboring a mutation (Ser15 to Phe) in ribosomal protein L7/L12 was isolated among revertants of a streptomycin-dependent strain. In the crystal structure of the L7/L12 dimer, residue 15 within the N-terminal domain contacts the C-terminal domain of the partner monomer. We tested effects of the mutation on molecular assembly by biochemical approaches. Gel electrophoretic analysis showed that the Phe15-L7/L12 variant had reduced ability in binding to L10, an effect enhanced in the presence of 0.05% of nonionic detergent. Mobility of Phe15-L7/L12 on gel containing the detergent was very low compared to the wild-type proteins, presumably because of an extended structural state of the mutant L7/L12. Ribosomes isolated from LL103 cells contained a reduced amount of L7/L12 and showed low levels (15-30% of wild-type ribosomes) of activities dependent on elongation factors and in translation of natural mRNA. The ribosomal activity was completely recovered by addition of an excess amount of Phe15-L7/L12 to the ribosomes, suggesting that the mutant L7/L12 exerts normal functions when bound on the ribosome. The interaction of Ser15 with the C-terminal domain of the partner molecule seems to contribute to formation of the compact dimer structure and its efficient assembly into the ribosomal GTPase center. We propose a model relating compact and elongated forms of L7/L12 dimers. Phe15-L7/L12 provides a new tool for studying the functional structure of the homodimer.
authors.affiliation: Institute of High Polymer Research, Faculty of Textile Science and Technology, Shinshu University, Ueda 386-8567, Japan.
authors.forename: Takaomi
authors.initials: T
authors.lastname: Nomura
authors.forename: Ruriko
authors.initials: R
authors.lastname: Mochizuki
authors.forename: Eric R
authors.initials: ER
authors.lastname: Dabbs
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Shimizu
authors.forename: Takuya
authors.initials: T
authors.lastname: Ueda
authors.forename: Akira
authors.initials: A
authors.lastname: Hachimori
authors.forename: Toshio
authors.initials: T
authors.lastname: Uchiumi
mesh_terms: D000595:Amino Acid Sequence; D019281:Dimerization; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D020558:GTP Phosphohydrolases; D008958:Models, Molecular; D010649:Phenylalanine / Q000235:genetics; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D012269:Ribosomal Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D012270:Ribosomes / Q000737:chemistry / Q000201:enzymology*; D012694:Serine / Q000235:genetics
chemical_list: D029968:Escherichia coli Proteins; D012269:Ribosomal Proteins; D012694:Serine; D010649:Phenylalanine; C016700:ribosomal protein L7-L12; D020558:GTP Phosphohydrolases