Question

Describe how CAP-cAMP is involved in the metabolism of maltose

Answer 1

Solution

1. The maltose regulon of Escherichia coli consists of three operons, malPQ, malK-lamB, and malEFG which are controlled by a positive regulatory gene, malT.
2. The full expression of this 3 regulon requires the action of cyclic AMP (cAMP) with of its receptor and the catabolite activator protein (CAP).
3. In deed, deletions of the gene crp, which codes for CAP, or of the gene cya, which codes for adenylate cyclase, result in a Mal- phenotype.
4. The malT expression was stimulated by cAMP and malT expression is controlled by CAP.
5. malT expression is stimulated by CAP and cAMP.
6. CAP and cAMP would enhance the affinity of the MalT protein for the promoter region of the mal EFG and malK-lamB and possibly of the malPQ operons.
7. In the absence of CAP, the affinity of the MalT protein for the malPQ promoter would be higher than that for the two other promoters.
8. In the presence of the CAP-cAMP complex, the affinity of the MalT protein for the malK-lamB and malEFG promoters would be higher than that for the malPQ promoter.