CiaRH represses comC and sthA in the ΔsdbA mutant. (A) Interaction between csRNA7 (52) and comC predicted by IntaRNA (53). The csRNA sequence was searched against the RefSeq sequence for S. gordonii Challis (GenBank accession no. NC_009785). The ribosomal binding site is underlined, and the box indicates the start codon. (B and C) Expression of comC and comE (B) and sthA (C) in the parent strain, the ΔsdbA mutant, the ΔciaRH mutant, and the ΔsdbA ΔciaRH mutant. (D) Bacteriocin activity of the parent strain, the ΔsdbA mutant, the ΔsdbA ΔdegP mutant, the sdbA-complemented mutant (SdbA Compl), the ΔciaRH mutant, the ΔsdbA ΔciaRH mutant, and the ciaRH-complemented mutant (ΔsdbA CiaRH Compl). Supernatants were filtered sterilized and inoculated with S. mitis as the target strain. Results are means ± SDs from three experiments. ****, P < 0.0001, compared with the parent strain; ***, P < 0.001, compared with the parent strain.