Corynebacterium diphtheria is the causal agent of the diseas

Corynebacterium diphtheria is the causal agent of the disease diphtheria. C diphtheria produces a toxin that can cause cell damage. The diphtheria toxin is only produced under low extra-cellular concentration of iron (commonly found in host cells). The tox genes are under negative control wherein a regulatory protein, (DtxR) binds to the operator region when iron is present. What kind of ligand is iron? Select one: O a. co-repressor o b. inducer O c. activator O d. repressor repressor How is DtxR functioning? Select one: O a. co-repressor O b. inducer O c. activator o d. repressor repressor What is happening in each cell (Cor D): are genes up-regulated, down-regulated, or neither? In the host with negligible iron (Fe): Not in the host, with iron plentiful: tox Fe tox Promoter operator Promoter Operator DtxR

Solution

1) Iron is a co-repressor.It causes repression of the toxin gene.

2) DTXR causes the repression of the DTX gene, by binding at the operator gene where iron helps it to bind to the operator region. Hence, it acts as a repressor.

3 and 4) In the cell C since there is no iron present hence th Dtx R gene product can not bind at the operator region of the Tox gene to prevent its transcription and thereby the translation is also not rpevented. Hence, the DTX R gene is downregulated while the Tox gene is upregulated.

In the cell D since there is a high concentration of iron present hence th Dtx R gene product can binds at the operator region of the Tox gene to prevent its transcription and thereby the translation. Hence, the DTX R gene is upregulated while the Tox gene is downregulated.

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