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). More than twofold more abundant in the large cell variant (LCV) stage than in the small cell variant (SCV) stage (at protein level). LCVs are more metabolically active than SCVs. Belongs to the bacterial ribosomal protein bS1 family.