Signal recognition particle

The signal recognition particle (SRP) is a common molecule found in cytoplasm. It is a "ribonucleoprotein" (a protein-RNA complex). It recognizes and targets specific proteins to the endoplasmic reticulum of eukaryotes and the plasma membrane of prokaryotes.
When the SRP-ribosome complex binds to a cell membrane receptor, SRP releases the ribosome and drifts away. The ribosome resumes protein synthesis, but now the protein is moving through the SRP-receptor transmembrane pore. So, SRP directs the movement of proteins within the cell. It binds with a transmembrane pore. This allows the protein to cross the membrane to where it is needed. In eukaryotes, the target is the membrane of the endoplasmic reticulum (ER).
The SRP is 'universally conserved'. That means it is so important that "all living things have it in their cells". Despite this, the actual composition of the SRP varies greatly between organisms.