SRP19

SRP19 is a small RNA-binding protein that is a component of the signal recognition particle (SRP). In archaea and in the chloroplasts of plants, SRP19 binds to SRP RNA and contributes to the assembly and stability of the SRP particle. It is not typically found in bacterial SRP, which uses a different complement of proteins and RNA.

In the SRP complex, SRP19 acts as an adaptor that recognizes a defined region of SRP RNA and helps recruit or stabilize the GTPase-containing subunit SRP54 (also called Ffh in some organisms). By stabilizing the SRP RNA structure, SRP19 facilitates efficient interaction of SRP54 with the SRP receptor, FtsY, at the target membrane, enabling cotranslational targeting of ribosome–nascent-chain complexes to the membrane.

SRP19 proteins are relatively small and show conservation of key RNA-binding residues across archaeal species, supporting a conserved role in SRP function. The presence and exact role of SRP19 can vary among organisms; some SRP systems can operate with altered or reduced SRP19 content, indicating evolutionary flexibility in SRP assembly.

Overall, SRP19 contributes to the fidelity and efficiency of cotranslational protein targeting by shaping SRP RNA structure and coordinating interactions among core SRP components during targeting.