Two amino acid residues from the DNA-binding domain of MalT play a crucial role in transcriptional activation.

MalT is the transcriptional activator of the Escherichia coli maltose regulon. Several lines of evidence suggest that MalT might act by interacting with RNA polymerase. Here, we show that 'MalT, the DNA-binding domain of MalT, activates transcription.

Multiple protein-DNA and protein-protein interactions are involved in transcriptional activation by MalT.

The promoters of the Escherichia coli maltose regulon are positively regulated by the MalT protein, which recognizes a short asymmetric nucleotide sequence that is present as several copies in each promoter of the regulon. We report a detailed biochemical characterization of the interaction of MalT with the promoter of the malPQ operon. The MalT sites in malPp were precisely located and their occupation as a function of MalT concentration was quantified using DNase I and dimethyl sulphate footprinting experiments.

Which nucleotides in the "-10" region are crucial to obtain a fully active MalT-dependent promoter?

We have replaced the hexanucleotide corresponding to the "-10" region of malPp, a positively regulated promoter from Escherichia coli, by random nucleotide sequences and isolated 48 different variants that were as active as the wild-type promoter. Analysis of the nucleotide sequence of their "-10" region strongly suggests that the nature of the nucleotide present at three positions plays a crucial role: 46 of the 48 malPp variants contained C or T at position -12, A at position -11 and T at position -7. The nucleotide composition at the three other positions seems to be much more flexible.

On the puzzling arrangement of the asymmetric MalT-binding sites in the MalT-dependent promoters.

The MalT-dependent promoters of the enterobacteria belong to a small family of positively regulated prokaryotic promoters in which the activator protein recognizes short asymmetric nucleotide sequences present in several locations and orientations. We demonstrate that active MalT-dependent semisynthetic promoters can be constructed by using a synthetic decanucleotide as the MalT site and random nucleotide sequences as connecting sequences, provided that the location and orientation of the sites are the same as in natural MalT-dependent promoters. Strikingly, the induced level of promoter activity and the induction factor of each semisynthetic promoter are identical to those of its natural counterpart, in spite of considerable differences in their nucleotide sequences.

A small C-terminal region of the Escherichia coli MalT protein contains the DNA-binding domain.

MalT, the transcriptional activator of the Escherichia coli maltose regulon, is a 901-amino acid-long protein that specifically binds to short, asymmetric nucleotide sequences present in several copies in the promoters of the regulon. We report that the protein structure involved in this specific binding is carried by a small C-terminal part of MalT encompassing the last 95 amino acid residues. This was demonstrated by fusing the last 95 codons of malT to the gene that encodes glutathione S-transferase, purifying the hybrid protein by affinity chromatography, and comparing the DNase I and dimethyl sulfate footprints of the hybrid and of wild-type MalT on different MalT-binding sites.