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Paper report

Real-time flagellar gene expression

Rachel Brem

Genome Biology 2001, 2:reports0024  doi:10.1186/gb-2001-2-8-reports0024

The electronic version of this article is the complete one and can be found online at: http://genomebiology.com/2001/2/8/reports/0024


Received:21 July 2001
Published:8 August 2001

© 2001 BioMed Central Ltd

Significance and context

The study of flagellar assembly in Escherichia coli began as a classical genetics question, but remains of biochemical interest today. One modern twist has been to study the order of expression of flagellar genes using DNA microarrays or lacZ reporter assays. Kalir et al. revisit the ordering problem with an in vivo assay for the expression of genes under the control of flagellar promoters using green fluorescent protein (GFP). Their results are more precise than those from previous studies and agree remarkably well with the known structure of the flagellum.

Key results

The authors transfected E. coli with plasmids encoding the amino-acid sequence of GFP, under the control of the promoter from a given flagellar operon. They diluted cultures out of stationary phase (in which bacteria do not manufacture new flagella) and measured GFP fluorescence over time from this zero point. After subjecting the time traces to a clustering algorithm, the authors ordered the clusters according to time of activation of the fluorescence curves. The cluster containing fliL and fliE - operons coding for the basal, intracellular components of the flagellum - reached high fluorescence levels first. Intermediate flagellar components were next; extracellular components were last, along with the 'navigation' elements meche and mocha, which operate in chemotaxis.

Links

The algorithm for ordering fluorescence traces is available at the home page of Uri Alon.

Conclusions

Kalir et al. conclude that the expression sequence of flagellar operons follows the flagellar structure itself. But this may not be the whole story. Previous work has shown that a flagellum can assemble even when expression order is scrambled. Kalir et al. suspect that the synchrony seen here may hinge on the dilution step of their experiment, in which the population of cells goes through a concerted change in medium conditions which may activate wholesale flagellar production.

Reporter's comments

Kalir et al. appear to have nailed down the expression order of flagellar operons. There are caveats, however. If the authors used a different clustering or ordering scheme, for example, or retooled the experiment to eliminate the dilution step, would they get the same results?

Table of links

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The full text and figures are available only to subscribers of the journal, but are available over the internet from the journal's website. The paper itself is abstracted by PubMed. There is no supplementary material.