One of the most prevalent sexually transmitted diseases is caused by the bacterium Chlamydia trachomatis and leads to blindness if left untreated. Upon infection, metabolically inert cells differentiate, through gene expression, to become metabolically active cells that divide by binary fission. It has been proposed that release from the inert state is dependent on heat-shock proteins that both activate the reproductive cycle and facilitate the binding of chlamydiae to host cells. Researchers made the following observations regarding the heat-shock regulatory system in Chlamydia trachomatis: (1) a regulator protein (call it R) binds to a cis-acting DNA element (call it \(\mathrm{D}\) ); (2) \(\mathrm{R}\) and \(\mathrm{D}\) function as a repressor- operator pair; (3) \(\mathrm{R}\) functions as a negative regulator of transcription; (4) \(\mathrm{D}\) is composed of an inverted-repeat sequence; (5) repression by \(R\) is dependent on \(D\) being supercoiled (Wilson \(\&\) Tan, 2002 ). (a) Based on this information, devise a model to explain the heat-dependent regulation of metabolism in Chlamydia trachomatis. (b) Some bacteria, like \(E .\) coli, use a heat-shock sigma factor to regulate heat-shock transcription. Are the above findings in Chlamydia compatible with use of a heat-sensitive sigma factor?

Step by step solution

01

Summarize Key Information

The given information about Chlamydia trachomatis: 1. A regulator protein (R) binds to a cis-acting DNA element (D). 2. R and D function as a repressor-operator pair. 3. R functions as a negative regulator of transcription. 4. D is composed of an inverted-repeat sequence. 5. Repression by R is dependent on D being supercoiled.

02

Devise a Model for Heat-Dependent Regulation of Metabolism

Based on the provided information, we can propose the following model for heat-dependent regulation of metabolism in Chlamydia trachomatis: 1. Under normal conditions, regulator protein R binds to the cis-acting DNA element D. 2. When R is bound to D, the transcription of metabolic genes is repressed due to the negative regulation of R. 3. Under heat-shock conditions, the binding of R and D is weakened or disrupted. 4. This disruption allows the transcription of metabolic genes to occur as the negative regulation by R is removed. 5. As transcription is no longer repressed, Chlamydia trachomatis cells become metabolically active and begin to reproduce.

03

Determine Compatibility with a Heat-Sensitive Sigma Factor

In E. coli and similar organisms, a heat-shock sigma factor helps regulate heat-shock transcription. This different sigma factor recognizes alternative promoters that will express genes needed for heat-shock response. Chlamydia trachomatis uses a repressor-operator system and the function of D seems to be dependent on its supercoiled state. Therefore, the involvement of a heat-sensitive sigma factor seems unlikely in this case, as its mode of action seems to be orthogonal to the repression-based mechanism observed here. However, we cannot completely rule out the possibility that Chlamydia trachomatis might employ additional regulatory systems, such as a heat-shock sigma factor, alongside the observed repressor-operator system.

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