A Point Mutation in Ribosomal Protein L7/L12 Reduces Its Ability to Form a Compact Dimer Structure and to Assemble into the GTPase Center

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• 作者：Takaomi Nomura ; Ruriko Mochizuki ; Eric R. Dabbs ; Yoshihiro Shimizu ; Takuya Ueda ; Akira Hachimori ; and Toshio Uchiumi
• 刊名：Biochemistry
• 出版年：2003
• 出版时间：April 29, 2003
• 年：2003
• 卷：42
• 期：16
• 页码：4691 - 4698
• 全文大小：182K
• 年卷期：v.42,no.16(April 29, 2003)
• ISSN：1520-4995

文摘

An Escherichia coli mutant, LL103, harboring a mutation (Ser15 to Phe) in ribosomal proteinL7/L12 was isolated among revertants of a streptomycin-dependent strain. In the crystal structure of theL7/L12 dimer, residue 15 within the N-terminal domain contacts the C-terminal domain of the partnermonomer. We tested effects of the mutation on molecular assembly by biochemical approaches. Gelelectrophoretic analysis showed that the Phe15-L7/L12 variant had reduced ability in binding to L10, aneffect enhanced in the presence of 0.05% of nonionic detergent. Mobility of Phe15-L7/L12 on gel containingthe detergent was very low compared to the wild-type proteins, presumably because of an extended structuralstate of the mutant L7/L12. Ribosomes isolated from LL103 cells contained a reduced amount of L7/L12and showed low levels (15-30% of wild-type ribosomes) of activities dependent on elongation factorsand in translation of natural mRNA. The ribosomal activity was completely recovered by addition of anexcess amount of Phe15-L7/L12 to the ribosomes, suggesting that the mutant L7/L12 exerts normalfunctions when bound on the ribosome. The interaction of Ser15 with the C-terminal domain of the partnermolecule seems to contribute to formation of the compact dimer structure and its efficient assembly intothe ribosomal GTPase center. We propose a model relating compact and elongated forms of L7/L12dimers. Phe15-L7/L12 provides a new tool for studying the functional structure of the homodimer.