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We describe the construction of six novel plasmid-based IPTG-inducible expression vectors for Bacillus subtilis and related species. While one vector allows intracellular production of recombinant proteins, the second provides a strong secretion signal. The third vector allows addition of the c-Myc epitope tag, and the remaining three vectors provide the purification tags His and Strep. The versatility of all six vectors was demonstrated by the insertion of several reporter genes and by their regulated overexpression. Recombinant proteins with a His- or Strep-tag could be purified to near homogeneity in a single step.

Nuclear receptor binding to coactivator proteins is an obligate first step in the regulation of gene transcription. Nuclear receptors preferentially bind to an LXXLL peptide motif which is highly conserved throughout the 300 or so natural coactivator proteins. This knowledge has shaped current understanding of this fundamental protein-protein interaction, and continues to inspire the search for new drug therapies. However, sequence specificity beyond the LXXLL motif and the molecular functioning of flanking residues still requires urgent addressing. Here, ribosome display has been used to reassess the estrogen receptor for new and enlarged peptide recognition motifs, leading to the discovery of a potent and highly evolved PXLXXLLXXP binding consensus. Molecular modeling and X-ray crystallography studies have provided the molecular insights on the role of the flanking prolines in priming the length of the α-helix and enabling optimal interactions of the α-helix dipole and its surrounding amino acids with the surface charge clamp and the receptor activation function 2. These findings represent new structural parameters for modulating the nuclear receptor-coactivator interaction based on linear sequences of proteinogenic amino acids and for the design of chemically modified inhibitors.