Sackett M J, Kelly A J, Brun Y V
Department of Chemistry, Indiana University, Bloomington 47405, USA.
Mol Microbiol. 1998 May;28(3):421-34. doi: 10.1046/j.1365-2958.1998.00753.x.
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.
细菌细胞分裂与DNA复制的协调机制仍然未知。我们利用易于同步化的新月柄杆菌来确定细胞分裂基因ftsQ和ftsA在DNA复制周期中的转录时间，并将它们的转录情况与ftsZ的转录情况进行比较。与大肠杆菌的情况不同，在新月柄杆菌中ftsQ和ftsA的转录并不延伸到ftsZ。ftsQ和ftsA由ftsQ上游ddl基因末端的一个强启动子P(QA)共同转录。P(QA)的转录在DNA复制期结束时开启，与ftsZ转录期的结束同步。ftsA还由位于ftsQ和ftsA之间的另一个启动子P(A)转录。P(A)的转录比P(QA)弱约10倍，且发生在DNA复制期。由P(A)转录ftsA足以维持细胞活力，但不足以进行正常的细胞分裂。当ftsA的转录持续增加时，细胞分裂受到抑制，并且在异常位置合成了柄。因此，ftsA和ftsZ的转录情况反映了它们在新月柄杆菌中的作用顺序，并且必须维持ftsA的正常转录以实现正常的细胞分裂和分化。
