Wikipedia
30S
30 S is the smaller subunit of the 70S ribosome of prokaryotes. It is a complex of ribosomal RNA and ribonucleoproteins that functions in mRNA translation. It includes the 16S ribosomal RNA. It has about 21 basic proteins.
The 30S subunit is the site of inhibition for antibiotics such as tetracycline and aminoglycosides.