Final answer:
If a protein binds to the ribosomal binding site in bacteria, it prevents the initiation of protein synthesis by blocking the assembly of the initiation complex, thus inhibiting gene expression and protein production.
Step-by-step explanation:
If a protein binds to the ribosomal binding site on an mRNA in bacteria, it will inhibit the initiation of protein synthesis. The ribosomal binding site, often referred to as the Shine-Dalgarno sequence in prokaryotes, is crucial for the small ribosomal subunit to bind and position the mRNA properly for translation initiation. When this site is blocked, the necessary components for translation, including the initiator tRNA and the large ribosomal subunit, cannot assemble, preventing the formation of a functional initiation complex. Consequently, the mRNA cannot be translated into a protein, affecting the bacterial cell's ability to express genes and synthesize essential proteins.