RESUMEN
The signal recognition particle (SRP), a protein-RNA complex conserved in all three kingdoms of life, recognizes and transports specific proteins to cellular membranes for insertion or secretion. We describe here the 1.8 angstrom crystal structure of the universal core of the SRP, revealing protein recognition of a distorted RNA minor groove. Nucleotide analog interference mapping demonstrates the biological importance of observed interactions, and genetic results show that this core is functional in vivo. The structure explains why the conserved residues in the protein and RNA are required for SRP assembly and defines a signal sequence recognition surface composed of both protein and RNA.
Asunto(s)
Proteínas Bacterianas/química , Proteínas de Escherichia coli , ARN Bacteriano/química , Partícula de Reconocimiento de Señal/química , Secuencia de Aminoácidos , Proteínas Bacterianas/metabolismo , Emparejamiento Base , Sitios de Unión , Membrana Celular/metabolismo , Cristalografía por Rayos X , Escherichia coli/química , Escherichia coli/genética , Escherichia coli/metabolismo , Guanosina Trifosfato/metabolismo , Enlace de Hidrógeno , Magnesio/metabolismo , Modelos Moleculares , Datos de Secuencia Molecular , Conformación de Ácido Nucleico , Potasio/metabolismo , Unión Proteica , Conformación Proteica , Estructura Secundaria de Proteína , Estructura Terciaria de Proteína , ARN Bacteriano/genética , ARN Bacteriano/metabolismo , Partícula de Reconocimiento de Señal/metabolismo , Transformación Bacteriana , Agua/metabolismoRESUMEN
Metal ions are essential for the folding and activity of large catalytic RNAs. While divalent metal ions have been directly implicated in RNA tertiary structure formation, the role of monovalent ions has been largely unexplored. Here we report the first specific monovalent metal ion binding site within a catalytic RNA. As seen crystallographically, a potassium ion is coordinated immediately below AA platforms of the Tetrahymena ribozyme P4-P6 domain, including that within the tetraloop receptor. Interference and kinetic experiments demonstrate that potassium ion binding within the tetraloop receptor stabilizes the folding of the P4-P6 domain and enhances the activity of the Azoarcus group I intron. Since a monovalent ion binding site is integral to the tetraloop receptor, a tertiary structural motif that occurs frequently in RNA, monovalent metal ions are likely to participate in the folding and activity of a wide diversity of RNAs.