9 research outputs found
Targets for the MalI repressor at the divergent Escherichia coliK-12malX-malI promoters
Random mutagenesis has been used to identify the target DNA sites for the MalI repressor at the divergent Escherichia coli K-12 malX-malI promoters. The malX promoter is repressed by MalI binding to a DNA site located from position -24 to position -9, upstream of the malX promoter transcript start. The malI promoter is repressed by MalI binding from position +3 to position +18, downstream of the malI transcript start. MalI binding at the malI promoter target is not required for repression of the malX promoter. Similarly, MalI binding at the malX promoter target is not required for repression of the malI. Although the malX and malI promoters are regulated by a single DNA site for cyclic AMP receptor protein, they function independently and each is repressed by MalI binding to a different independent operator site
A Transcriptional āScreamā Early Response of E. coli Prey to Predatory Invasion by Bdellovibrio
We have transcriptionally profiled the genes differentially expressed in E. coli prey cells when predatorily attacked by Bdellovibrio bacteriovorus just prior to prey cell killing. This is a brief, approximately 20ā25Ā min period when the prey cell is still alive but contains a Bdellovibrio cell in its periplasm or attached to and penetrating its outer membrane. Total RNA was harvested and labelled 15Ā min after initiating a semi-synchronous infection with an excess of Bdellovibrio preying upon E. coli and hybridised to a macroarray spotted with all predicted ORFs of E. coli. SAM analysis and t-tests were performed on the resulting data and 126 E. coli genes were found to be significantly differentially regulated by the prey upon attack by Bdellovibrio. The results were confirmed by QRT-PCR. Amongst the prey genes upregulated were a variety of general stress response genes, potentially āselfishā genes within or near prophages and transposable elements, and genes responding to damage in the periplasm and osmotic stress. Essentially, the presence of the invading Bdellovibrio and the resulting damage to the prey cell elicited a small ātranscriptional screamā, but seemingly no specific defensive mechanism with which to counter the Bdellovibrio attack. This supports other studies which do not find Bdellovibrio resistance responses in prey, and bodes well for its use as a āliving antibioticā
X-ray structure of MalY from Escherichia coli: a pyridoxal 5ā²-phosphate-dependent enzyme acting as a modulator in mal gene expression
MalY represents a bifunctional pyridoxal 5ā²-phosphate-dependent enzyme acting as a Ī²ācystathionase and as a repressor of the maltose regulon. Here we present the crystal structures of wild-type and A221V mutant protein. Each subunit of the MalY dimer is composed of a large pyridoxal 5ā²-phosphate-binding domain and a small domain similar to aminotransferases. The structural alignment with related enzymes identifies residues that are generally responsible for Ī²ālyase activity and depicts a unique binding mode of the pyridoxal 5ā²āphosphate correlated with a larger, more flexible substrate-binding pocket. In a screen for MalY mutants with reduced mal repressor properties, mutations occurred in three clusters: I, 83ā84; II, 181ā189 and III, 215ā221, which constitute a clearly distinguished region in the MalY crystal structure far away from the cofactor. The tertiary structure of one of these mutants (A221V) demonstrates that positional rearrangements are indeed restricted to regions I, II and III. Therefore, we propose that a direct proteināprotein interaction with MalT, the central transcriptional activator of the maltose system, underlies MalY-dependent repression of the maltose system