4. A quorum sensing response in organism X results in upregulation of one gene (

Question

4. A quorum sensing response in organism X results in upregulation of one gene (gsgl) and downregulation of another (gsg2). Assume that preliminary experiments have shown that homoserine lactone functions as the autoinducer for this response. You are interested in how quorum sensing is regulated in this organism and you have isolated a mutant strain that is no longer able to upregulate qsgl and downregulate qsg2 when treated with homoserine lactone. You find that this mutant strain fails to produce a single protein that is present in the wildtype strain due to a frameshift mutation within a particular gene (qsg3). Based on the various mechanisms of gene regulation discussed in class, propose a mechanism for how qsgl and qsg2 expression is regulated. Describe at the molecular level all elements and allosteric interactions that your proposed mechanism requires. There is not a unique answer to this question; multiple combinations of repressors and/or activators and/or small RNAs etc can be invoked. Your answer should be detailed but concisc 44 F7 FS 4

Explanation / Answer

According to the information, gene 1 is up-regulated whereas gene 2 is down regulated in the presence of gene 3. Further, homoserine lactone remains a positive regulator for this sequential event. Hence, under normal conditions, gene 3 must reside upstreams gene 1 and finally gene 2 must be localized most downstream in the cistron. Otherwise, the gene 2 can be localized trans to gene 2 in order to undergo reverse expression as compared to gene 1. Hence, the localization of the three genes can be found as below:

Gene 3 - Gene 1/Trans Gene 2.

As a mode of action, the gene 3 is a positive regulator or performs regulator-like function whereas gene 2 acts in trans with respect to gene 1. These two genes/gene products are antagonist to each other in this case.

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