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Diverse molecules, from small antibacterial drugs to large protein toxins, are exported directly across both cell membranes of gram-negative bacteria. This export is brought about by the reversible interaction of substrate-specific inner-membrane proteins with an outer-membrane protein of the TolC family, thus bypassing the intervening periplasm. Here we(More)
The coordinated regulation of gene expression is required for homeostasis, growth and development in all organisms. Such coordination may be partly achieved at the level of messenger RNA stability, in which the targeted destruction of subsets of transcripts generates the potential for cross-regulating metabolic pathways. In Escherichia coli, the balance and(More)
Two crystal structures of the glucocorticoid receptor DNA-binding domain complexed with DNA are reported. The domain has a globular fold which contains two Zn-nucleated substructures of distinct conformation and function. When it binds DNA, the domain dimerizes, placing the subunits in adjacent major grooves. In one complex, the DNA has the symmetrical(More)
Poly(dA).poly(dT) has unusual properties in that it cannot associate into nucleosomes and short, phased runs of it cause DNA bending. The crystal structure of a B-type DNA dodecamer containing a homopolymeric run of six A.T base pairs shows that this region possesses special structural features, including a system of bifurcated hydrogen bonds, which(More)
The crystal structure of the trp repressor/operator complex shows an extensive contact surface, including 24 direct and 6 solvent-mediated hydrogen bonds to the phosphate groups of the DNA. There are no direct hydrogen bonds or non-polar contacts to the bases that can explain the repressor's specificity for the operator sequence. Rather, the sequence seems(More)
BACKGROUND Polynucleotide phosphorylase (PNPase) is a polyribonucleotide nucleotidyl transferase (E.C.2.7.7.8) that degrades mRNA in prokaryotes. Streptomyces antibioticus PNPase also assays as a guanosine 3'-diphosphate 5'-triphosphate (pppGpp) synthetase (E.C.2.7.6.5). It may function to coordinate changes in mRNA lifetimes with pppGpp levels during the(More)
Repeat tracts of guanine bases found in DNA and RNA can form tetraplex structures in the presence of a variety of monovalent cations. Evidence suggests that guanine tetraplexes assume important functions within chromosomal telomeres, immunoglobulin switch regions, and the human immunodeficiency virus genome. The structure of a parallel-stranded tetraplex(More)
A recently identified sequence motif, referred to as "C3HC4" (also "RING finger" and "A Box") for its distinctive pattern of putative metal-binding residues, has been found in a wide range of proteins. In a previous paper we described the expression and purification of fragments encompassing this motif from the Vmw110 (IPC0) protein family. We showed that(More)
Hfq is an RNA-binding protein that is common to diverse bacterial lineages and has key roles in the control of gene expression. By facilitating the pairing of small RNAs with their target mRNAs, Hfq affects the translation and turnover rates of specific transcripts and contributes to complex post-transcriptional networks. These functions of Hfq can be(More)
Ribonuclease E is an essential hydrolytic endonuclease in Escherichia coli, and it plays a central role in maintaining the balance and composition of the messenger RNA population. The enzyme is also required for rRNA and tRNA processing. We have shown earlier that the highly conserved catalytic domain of E. coli RNase E is a homotetramer [Callaghan, A. J.(More)