Binds mRNA; thus facilitating recognition of the initiation point. It is needed to translate mRNA with a short Shine-Dalgarno (SD) purine-rich sequence (By similarity). Part of the 30S ribosomal subunit. Some nascent polypeptide chains are able to cross-link to this protein in situ. Can be cross-linked to mRNA in the ribosome (By similarity). Phosphorylated; probably on a serine. Belongs to the bacterial ribosomal protein bS1 family.