A point mutation in ribosomal protein L7/L12 reduces its ability to form a compact dimer structure and to assemble into the GTPase center

Takaomi Nomura, Ruriko Mochizuki, Eric R. Dabbs, Yoshihiro Shimizu, Takuya Ueda, Akira Hachimori, Toshio Uchiumi

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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.

Original languageEnglish
Pages (from-to)4691-4698
Number of pages8
JournalBiochemistry
Volume42
Issue number16
DOIs
Publication statusPublished - 2003 Apr 29
Externally publishedYes

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ASJC Scopus subject areas

  • Biochemistry

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