Essential and nonessential sequences in malPp, a positively controlled promoter in Escherichia coli.

A plasmid bearing the malPp promoter was digested with Bal31 to obtain a set of deletions with closely spaced endpoints in the upstream region of this promoter. Some of these deletions were sequenced, and their effect on malPQ expression was determined after having transferred them onto the chromosome. We found that a site which binds the cyclic AMP receptor protein in vitro and which is centered at position -93 with respect to the site of transcription initiation could be deleted without affecting malPQ expression. In contrast, the activity of the malPp promoter decreased abruptly when the deletions reached position -72. The downstream region of the promoter was analyzed by using a technique of "sequence replacement" which involved the selection of Mal+ pseudorevertants from strains which carried small deletions in the -25 region. The pseudorevertants, which expressed the malPQ operon in a manner indistinguishable from wild type, had grossly different sequences downstream from position -38, except for a few positions, some of which must be important for promoter function. By combining all presently available information, it is suggested that the malPp promoter contains three binding sites for its activator, the product of gene malT. These sites are defined by three quasi-identical hexanucleotides present in one orientation around position -37 and twice in the other orientation around positions -60 and -73.