Evolutionarily conserved binding of ribosomes to the translocation channelvia the large ribosomal RNA

During early stages of cotranslational protein translocation across the end oplasmic reticulum (ER) membrane the ribosome is targeted to the heterotrim eric Sec61p complex, the major component of the protein-conducting channel. We demonstrate that this interaction is mediated by the 28S rRNA of the eu karyotic large ribosomal subunit. Bacterial ribosomes also bind via their 2 3S rRNA to the bacterial homolog of the Sec61p complex, the SecYEG complex. Eukaryotic ribosomes bind to the SecYEG complex, and prokaryotic ribosomes to the Sec61p complex. These data indicate that rRNA-mediated interaction of ribosomes with the translocation channel occurred early in evolution and has been conserved.