Transcriptional analysis of the gene encoding pyruvate formate-lyase-activating enzyme of Escherichia coli

The act gene of Escherichia coli encodes the pyruvate formate-lyase-activating enzyme which is necessary for the post-translational modification of pyruvate formate-lyase. The gene is located 191 bp downstream from the pfl structural gene. Northern blot analysis revealed that the act transcript is monocistronic and that transcription is independent of pfl gene expression. Through mapping of the 5' and 3' ends of the act transcript, sequences could be identified showing similarity to both an Escherichia coli sigma 70 promoter and to a rho-independent transcription terminator. Expression of the act gene was analysed with the aid of chromosomally integrated transcriptional and translational lacZ fusions. The results verified that the act gene is transcribed from its own promoter and that expression of the gene is essentially constitutive. Anaerobiosis led only to a two-fold increase in expression over that observed in aerobically grown cells and this elevated expression was independent of the transcriptional regulator, Fnr. Moreover, effectors such as pyruvate and nitrate, which substantially influence anaerobic transcription of the pfl gene, did not affect act gene expression.