On the role of the multiple regulatory elements involved in the activation of the Escherichia coli malEp promoter.

Activation of malEp and malKp, two divergent promoters from Escherichia coli, depends on the synergistic action of MalT and CRP. The reaction involves a common regulatory region located in between and comprising multiple binding elements for both regulatory proteins. The binding of MalT and CRP to this region is known to result in the formation of a higher-order structure that is responsible for malKp activation. This paper presents genetic data which together with previous results, provide compelling evidence that this higher-order structure is also responsible for malEp activation. The role(s) that this structure or elements thereof play in the activation of malEp is analysed by monitoring both the occupancy of the proximal MalT sites (sites 1 and 2) and the activity of different malEp variants in strains containing increasing amounts of active MalT. A truncated malEp promoter comprising only MalT sites 1 and 2 forms a minimal MalT-dependent promoter whose activity is limited by the occupancy of these sites. One role of the higher-order structure formed by MalT and CRP when bound to the entire regulatory region is to ensure high occupation of MalT sites 1 and 2, but it is not its only function. Some elements of this structure, namely the CRP site 1, located at -76.5, and the distal MalT sites, seem to play a direct role in malEp activation besides their participation in the assembly of the higher-order structure.