Signal recognition particle (SRP) does not mediate a translational arrest of nascent secretory proteins in mammalian cell-free systems.

The ability of the signal recognition particle (SRP) to induce translational arrests in wheat germ, reticulocyte and HeLa cell-free translation systems was examined. In accordance with published data, SRP caused a complete arrest of secretory protein (IgG light chain) translation in wheat germ. In contrast, SRP had no effect on translation in either reticulocyte or HeLa cell lysates, even at 5-fold higher SRP levels than needed for complete arrest in wheat germ. The existence of a "docking-protein-like" releasing activity was ruled out, in the case of reticulocyte lysate, by experiments in which reticulocyte subfractions were added to blocked translations in wheat germ. In the absence of additional evidence to the contrary, it seems as if the translational arrest is peculiar to the wheat germ cell-free system.