Signal Sequence Cleavage of Peptidyl-tRNA Prior to Release from the Ribosome and Translocon

Many secretory polypeptides undergo cleavage of their signal sequence. In this study, we observed and quantitated the presence of a tRNA-bound, ribosome-associated polypeptide subpopulation present in vitro. This subpopulation was accessible to signal peptidase on ribosome-associated polypeptides longer than 114 amino acids. This demonstrates that it is possible for a peptidyl-tRNA species, in the midst of translation, to be processed by the endoplasmic reticulum signal peptidase implying that the peptidase is closely associated with the mammalian translocon.