RESUMO
Ribosomal RNA (rRNA) modifications are essential for ribosome function in all cellular organisms. Box C/D small (nucleolar) ribonucleoproteins [s(no)RNPs] catalyze 2'-O-methylation, one rRNA modification type in Eukarya and Archaea. Negatively stained electron microscopy (EM) models of archaeal box C/D sRNPs have demonstrated the dimeric sRNP (di-sRNP) architecture, which has been corroborated by nuclear magnetic resonance (NMR) studies. Due to limitations of the structural techniques, the orientation of the box C/D sRNAs has remained unclear. Here, we have used cryo-EM to elucidate the sRNA orientation in a M. jannaschii box C/D di-sRNP. The cryo-EM reconstruction suggests a parallel orientation of the two sRNAs. Biochemical and structural analyses of sRNPs assembled with mutant sRNAs indicate a potential interaction between the sRNA stem ends. Our results suggest that the parallel arrangement of the sRNAs juxtaposes their stem ends into close proximity to allow for a stabilizing interaction that helps maintain the di-sRNP architecture.
Assuntos
Conformação de Ácido Nucleico , RNA Ribossômico/química , RNA Ribossômico/metabolismo , Ribonucleoproteínas Nucleolares Pequenas/metabolismo , Archaea/genética , Microscopia Crioeletrônica , Espectroscopia de Ressonância Magnética , Metilação , Modelos Moleculares , Mutação , Ligação Proteica , Conformação Proteica , Estabilidade de RNA , Transporte de RNA , RNA Arqueal/química , RNA Arqueal/genética , RNA Ribossômico/genéticaRESUMO
Given that ribosomes are one of the most important cellular macromolecular machines, it is not surprising that there is intensive research in ribosome biogenesis. Ribosome biogenesis is a complex process. The maturation of ribosomal RNAs (rRNAs) requires not only the precise cleaving and folding of the pre-rRNA but also extensive nucleotide modifications. At the heart of the processing and modifications of pre-rRNAs in Archaea and Eukarya are ribonucleoprotein (RNP) machines. They are called small RNPs (sRNPs), in Archaea, and small nucleolar RNPs (snoRNPs), in Eukarya. Studies on ribosome biogenesis originally focused on eukaryotic systems. However, recent studies on archaeal sRNPs have provided important insights into the functions of these RNPs. This paper will introduce archaeal rRNA gene organization and pre-rRNA processing, with a particular focus on the discovery of the archaeal sRNP components, their functions in nucleotide modification, and their structures.