The small ribonucleoprotein component of RIBOSOMES. It contains the MESSENGER RNA binding site and two TRANSFER RNA binding sites - one for the incoming AMINO ACYL TRNA (A site) and the other (P site) for the peptidyl tRNA carrying the elongating peptide chain.

Synonyms: Subunits, Small Ribosomal Small Ribosomal Subunit Ribosomal Subunits, Small Small Ribosomal Subunits Small Ribosome Subunits Subunit, Small Ribosome Subunits, Small Ribosome Ribosome Subunits, Small Small Ribosome Subunit Ribosomal Subunit, Small Ribosome Subunit, Small Subunit, Small Ribosomal