Structures of ribonucleoprotein particle modification enzymes

Small nucleolar and Cajal body ribonucleoprotein particles (RNPs) are requiredfor the maturation of ribosomes and spliceosomes. They consist of small nucleolar RNAor Cajal body RNA combined with partner proteins and represent the most complex RNAmodification enzymes. Recent advances in structure and function studies have revealeddetailed information regarding ribonucleoprotein assembly and substrate binding. Theseenzymes form intertwined RNA–protein assemblies that facilitate reversible binding of thelarge ribosomal RNA or small nuclear RNA. These revelations explain the specificity amongthe components in enzyme assembly and substrate modification. The multiple conformationsof individual components and those of complete RNPs suggest a dynamic assembly processand justify the requirement of many assembly factors in vivo