Crystal structure of the S15-rRNA complex

In bacterial ribosomes, the small (30S) ribosomal subunit is composed of 16 S rRNA and 21 distinct proteins, Ribosomal protein S15 is of particular int erest because it binds primarily to 16S rRNA and is required for assembly o f the small subunit and for intersubunit association, thus representing a k ey element in the assembly of a whole ribosome. Here we report the 2.8 Angs trom resolution crystal structure of the highly conserved S15-rRNA complex Protein S15 interacts in the minor groove with a G-U/G-C motif and a three- way junction. The latter is constrained by a conserved base triple and stac king interactions, and locked into place by magnesium ions and protein side chains, mainly through interactions with the unique three-dimensional geom etry of the backbone. The present structure gives insights into the dual ro le of S15 in ribosome assembly and translational regulation.