Binds as a heterodimer with protein S6 to the central domain of the 16S rRNA, where it helps stabilize the platform of the 30S subunit. Part of the 30S ribosomal subunit (PubMed:30126986). Forms a tight heterodimer with protein S6 (By similarity). Strongly expressed during exponential growth, decreases 2-4-fold in stationary phase, part of the rpsF-ssbA-rpsR operon (PubMed:14762004). The operon is induced by DNA damage by mitomycin C (PubMed:14762004). Belongs to the bacterial ribosomal protein bS18 family. Extended N-terminus.