ORDERED EXPRESSION OF FTSQA AND FTSZ DURING THE CAULOBACTER-CRESCENTUS CELL-CYCLE

The mechanisms by which bacterial cell division and DNA replication ar e co-ordinated are still unknown. We have used the easily synchronizab le bacterium Caulobacter crescentus to determine when the cell divisio n genes ftsQ and ftsA are transcribed during the DNA replication cycle and to compare their transcription with that of ftsZ. Unlike the situ ation in Escherichia coli, transcription of ftsQ and ftsA does not ext end into ftsZ in Caulobacter. ftsQ and ftsA are co-transcribed by a st rong promoter, P-QA, present within the end of the ddl gene upstream o f ftsQ. Transcription of P-QA is turned on at the end of the DNA repli cation period, coincident with the end of the ftsZ transcription perio d. ftsA is also transcribed by another promoter, P-A, present between ftsQ and ftsA. P-A transcription is approximate to 10 times weaker tha n P-QA and occurs during the DNA replication period. Transcription of ftsA by P-A is sufficient for cell viability, but is not sufficient fo r normal cell division. When the transcription of ftsA is increased co nstitutively, 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 t o be maintained for normal cell division and differentiation.