Structure and Function of Signal Recognition Particle RNA

This chapter describes the structure and function of the RNA component of the signal recognition particle (SRP). It starts with a brief description of the function of SRP in the process of translocation of secretory proteins across the membrane of the endoplasmic reticulum. Then, all known SRP-RNA sequences are compared to form a solid basis for a common secondary structure. This is followed by a discussion on intramolecular interactions that might be responsible for the folding of the SRP-RNA into a three-dimensional molecule and on the dynamic property of the RNA. The SRP appears as an elongated rod with terminal small and large globular domains. This bone-like structure is consistent with the finding that at least two functions can be attributed to SRP: the effect on translation (which resides in the small domain, containing the Alu parts of the RNA, and the 9-kDa/l4-kDa protein dimer) and the effect on protein translocation itself. Finally, an attempt is made to bring the two partners of the SRP into the picture: the translating ribosome, and the membrane of the endoplasmic reticulum.