S15
Ribosomal protein S15 is a highly basic four alpha helix bundle. It binds primarily to the central domain of 16S rRNA and is necessary for assembly of the 30S subunit, as well as the association between subunits. The junction between the protein and rRNA is bound by a C-G*G base triple, "cross strand stacking", and magnesium ions. The amino terminal of one helix extends away from the other three alpha helices, which form the core of the protein. It is proposed that the tertiary structure between helixes 20,21, and 22 is dependent on S15 binding, as the angle between these helices is ~120° in the absence of S15. S15 is also involved in translation regulation.
(Agalarov, 2000)
(Nikulin, 2000)

S17
S17 is a 10.0 kDa 16s rRNA primary binding protein. It is required for assembly of the small ribosomal subunit and contributes to translational fidelity. S17 consists of five beta strands that are arranged in an antiparallel sheet. It is proposed that the main function of S17 is to lock the region of 16S rRNA it binds to, helices 7 and 11, into a certain conformation. It also interacts with helix 21, and forms crosslinks with proteins S4 and S13.
(Golden, 1993)

S20
S20 binds in the lower part of the 30S subunit and crosslinks to S12. It is comprised of three alpha helices that form one globular domain.
(Wimberly, 2000)