S14
S14 forms a cluster with the proteins S3 and S10 by hydrophobic interactions. It fits into an RNA gap in the head, being a stabilizing force in the structure. Furthermore, it interacts with the C-terminal tail of S9, linking the proteins, which are on opposite sides of a region, thus helping to lock the structure into place.
(Wimberly, 2000)

S21
The S21 protein is that final protein to bind to the assembling 30s subunit. It targets the central domain of the 16S rRNA. Not much is known about the structure of S21. It is known that it crosslinks to S13, S11, S12, S18. These crosslinks were determined using diagonal and two-dimensional electrophoresis.
(Lambert, 1983)
(Sommer, 1976)