The spo0K (opp) operon of Bacillus subtilis encodes an oligopeptide permease that is required for uptake of oligopeptides, development of genetic competence, and initiation of sporulation. We made in-frame, non-polar deletion mutations in each of the first four genes of the five-gene spo0K operon and tested effects on oligopeptide transport, sporulation, and expression of competence genes. spo0KA, B, C, and D were required for sporulation, competence development, and oligopeptide transport. Disruption of spo0KE caused a less severe phenotype than did disruption of any of the other genes of the operon.