RPSL

rpsL is a gene found in bacteria that encodes ribosomal protein S12, a component of the small (30S) ribosomal subunit. S12 is essential for the accuracy of translation, contributing to decoding fidelity at the ribosome’s decoding center by helping monitor codon–anticodon interactions with the 16S rRNA. The gene is typically located on the bacterial chromosome and is conserved across many bacterial species.

Mutations in rpsL are among the most well-characterized determinants of resistance to the aminoglycoside antibiotic streptomycin. These mutations often alter contact points between streptomycin and the ribosome, reducing the drug’s ability to bind and thereby conferring resistance. While such mutations can provide high-level resistance, they frequently impose a fitness cost on the organism in the absence of antibiotic, a drawback that can be offset by compensatory changes in other ribosomal components or in rRNA.

Because of its role in antibiotic resistance and genetic selection, rpsL is used as a selectable marker in molecular genetics. In streptomycin-based selection systems, introducing a wild-type rpsL allele can restore drug sensitivity, enabling counterselection approaches that rely on the presence or absence of resistance.

rpsL has homologs in a broad range of bacteria and is functionally related to ribosomal protein S12 in other organisms. In clinical microbiology, rpsL mutations are a known mechanism of streptomycin resistance in pathogens such as Mycobacterium tuberculosis, illustrating the gene’s relevance to antibiotic resistance and bacterial evolution.