Crystal structure of the ribonucleoprotein core of the signal recognition particle

The signal recognition particle (SRP), a protein-RNA complex conserved in a ll three kingdoms of Life, recognizes and transports specific proteins to c ellular membranes for insertion or secretion. We describe here the 1.8 angs trom 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, a nd genetic results show that this core is functional in vivo. The structure explains why the conserved residues in the protein and RNA are required fo r SRP assembly and defines a signal sequence recognition surface composed o f both protein and RNA.