The Spo0A regulatory protein controls the onset of stationary phase and sporulation by controlling transcription in both a negative and a positive manner depending on the promoter affected. Missense mutations, e.g., spo0A9V, which result in alterations in the eleventh amino acid preceding the C terminus of the Spo0A protein, give rise to a protein active as a negative regulator of the abrB gene but unable to activate transcription of the spoIIA gene. Second-site suppressors of spo0A9V occurred within the spo0A gene at codons 162 and 174. These suppressors did not suppress a spo0F mutation, indicating that the suppressed protein still requires phosphorylation for activity. The results suggest that the C terminus of Spo0A interacts with the transcription complex to activate transcription.