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Division takes place once growth has doubled all the cellular components
Mass, DNA and every single component of the cell increases during growth. Once duplication of all of them is achieved the cell is ready for division.Many genes whose products are involved in septation or in cell wall elongation are clustered in the Escherichia coli genomeSeptation has to be initiated and finalised for division to be effective. The building blocks of the septum should be produced to allow their assembly not only at the correct place, but also at the correct time.
The dcw cluster is conserved in many bacteria.
The expression of genes in the dcw cluster is regulated by a complex set of signals.
The natural regulatory signals within the dcw cluster are needed for the correct functioning of cell divisionThe dcw cluster contains many promoters and no transcriptional terminator. It would be possible that a single comprehensive transcript could represent the whole message of the cluster. In addition partial transcripts can be initiated from several promoters, some of them located inside structural regions of genes.
We can estimate the contribution of some individual promoter s to the transcription of the distal ftsZ gene, the one that codes for the "universal" cell division protein FtsZ.
This diagram depicts the expression of ftsZas a river, indicating the relative amount of flow contributed to the stream by each promoter (or set of promoters) in the nearby upstream genes. A large portion of the flow originates further upstream, likely at promoters in the upstream part of the dcwcluster.
- K. Flärdh, T. Garrido, and M. Vicente. 1997. Contribution of individual promoters in the ddlB - ftsZ region to the transcription of the essential cell-division gene ftsZ in Escherichia coli. Mol. Microbiol. 24: 927-936.
- K. Flärdh, P. Palacios and M. Vicente. 1998. Cell division genes ftsQAZin Escherichia coli require distant cis-acting signals upstream ddlB for full expression. Mol. Microbiol. 30: 305-315.
-Cam, K., Rome, G., Krisch, H. M., and Bouché, J.-P. (1996) RNase E processing of essential cell division genes mRNA in Escherichia coli. Nucleic Acids Res 24: 3065-3070.
This is demonstrated by the behaviour of a strain, VIP205, in which the ftsZ gene in the chromosome is artificially driven by an inducible promoter.
At time 0 these VIP205 cells have been transferred to a medium in which the amount of FtsZ produced is 80% the amount found in the wild type. They miss some divisions and become longer (at 140 and 180 min). When division resumes at the initial rate (at 220 min), they are nevertheless twice as long as they were at time 0 .
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last update: 24 April 2000
