Structure and expression of the cell division genes ftsQ, ftsA and ftsZ

The essential cell division genes ftsQ, ftsA and ftsZ map in a cluster of cell envelope genes located at two minutes on the Escherichia coli genetic map and appear to constitute an atypical operon. These closely clustered genes are all transcribed in the same direction and yet each of these genes was independently cloned on a multicopy plasmid and found to be expressed. Tn5 insertion mutagenesis of this region confirmed that these genes were independently expressed, indicating that each of these genes has its own promoter. However, maximum expression of the distal ftsZ gene required the promoter for the proximal ftsQ gene. The proximal ftsZ promoter was located within the ftsA structural gene and the proximal ftsA promoter was located within the ftsQ structural gene. No transcription terminators were evident from the DNA sequence analysis of this region. The sequence analysis also revealed that the termination codon for ftsQ overlapped the initiation codon of the ftsA gene and that the ftsA and ftsZ genes were separated by 60 base-pairs. The ftsQ gene product has a calculated Mr of 31,432 and the ftsA gene product has a calculated Mr of 45,327. The structure and expression of these genes are discussed.