Ordered expression of ftsQA and ftsZ during the Caulobacter crescentus cell cycle

The mechanisms by which bacterial cell division and DNA replication are co-ordinated are still unknown. We have used the easily synchronizable bacterium Caulobacter crescentus to determine when the cell division genes ftsQ and ftsA are transcribed during the DNA replication cycle and to compare their transcription with that of ftsZ. Unlike the situation in Escherichia coli, transcription of ftsQ and ftsA does not extend into ftsZ in Caulobacter. ftsQ and ftsA are co-transcribed by a strong promoter, P(QA), present within the end of the ddl gene upstream of ftsQ. Transcription of P(QA) is turned on at the end of the DNA replication period, coincident with the end of the ftsZ transcription period. ftsA is also transcribed by another promoter, P(A), present between ftsQ and ftsA. P(A) transcription is approximately 10 times weaker than P(QA) and occurs during the DNA replication period. Transcription of ftsA by P(A) is sufficient for cell viability, but is not sufficient for normal cell division. When the transcription of ftsA is increased constitutively, cell division is inhibited and stalks are synthesized at aberrant positions. Thus, transcription of ftsA and ftsZ mimics their order of action in Caulobacter and proper transcription of ftsA has to be maintained for normal cell division and differentiation.