Structural basis for the interaction of protein S1 with the Escherichia coli ribosome

In Gram-negative bacteria, the multi-domain protein S1 is essential for translation initiation, as it recruits the mRNA and facilitates its localization in the de-coding centre. In sharp contrast to its functional im-portance, S1 is still lacking from the high-resolution structures available for Escherichia coli and Ther-mus thermophilus ribosomes and thus the molec-ular mechanism governing the S1–ribosome inter-action has still remained elusive. Here, we present the structure of the N-terminal S1 domain D1 when bound to the ribosome at atomic resolution by us-ing a combination of NMR, X-ray crystallography and cryo-electron microscopy. Together with biochemi-cal assays, the structure reveals that S1 is anchore