Use of deletions created in vitro to map transcriptional regulatory signals in the malA region of Escherichia coli.

The malA region of Escherichia coli contains one of the three maltose operons, namely malPQ, and the positive regulatory gene, malT. Gene malT and the malPQ operon are transcribed in opposite directions, in a divergent manner. The distance separating the transcription start-points in the two directions was previously shown to be 513 base-pairs. We are now presenting a deletion analysis of this unexpectedly long intergenic region. Two sets of deletions were created in vitro, by using exonuclease BAL31. One set comprised deletions centered on a HincII restriction site located in the malPQ promoter, and extending towards gene malT. The other set was centered on an EcoRI site, which had been introduced close to the beginning of the malT cistron, and extended towards gene malP. These deletions, initially created on plasmids, were transferred onto the bacterial chromosome. By studying the phenotype resulting from the presence of these deletions, we concluded that: (1) all of the DNA sequences required for expression of malT and malPQ are within 100 base-pairs of the respective transcription start-points for these genes; (2) a sequence located more than 120 base-pairs upstream from the malT transcription start-point plays a role in limiting malT expression; and (3) a remaining DNA segment, 150 to 300 base-pairs in length, and centrally located in the inter-promoter region, seems to play no role in the expression of malT or malPQ.