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Integration of Environmental Signals Controls Expression of Bordetella Heme Utilization Genes. Carin K. Vanderpool, 2004. The Bordetella pertussis heme utilization gene cluster hurIR bhuRSTUV encodes regulatory and transport functions required for assimilation of iron from heme and hemoproteins . Expression of the bhu genes is iron regulated and heme inducible . The putative extracytoplasmic function [ECF] 
factor, HurI, is required forheme-responsive bhu gene
expression . In this study, transcriptionalactivation of B .
pertussis bhu genes in response to heme compoundswas shown to be
dose dependent and specific for heme; protoporphyrinIX and other
heme structural analogs did not activate bhu geneexpression .
Two promoters controlling expression of the hemeutilization genes
were mapped by primer extension analysis.The hurI promoter
showed similarity to
70-like
promoters, andits transcriptional activity was iron regulated and
heme independent.A second promoter identified upstream of bhuR
exhibited littlesimilarity to previously characterized ECF
factor-dependentpromoters . Expression of bhuR was iron
regulated, heme responsive,and hurI dependent in B .
pertussis, as shown in a previous studywith Bordetella
bronchiseptica . Further analyses showed thattranscription
originating at a distal upstream site and readingthrough the
hurR-bhuR intergenic region contributes to bhuRexpression
under iron starvation conditions in the absence ofheme inducer . The
pattern of regulation of the readthrough transcriptwas consistent
with transcription from the hurI promoter . Thepositions and
regulation of the two promoters within the hur-bhugene
cluster influence the production of heme transport machineryso that
maximal expression of the bhu genes occurs under iron
starvation conditions only in the presence of heme iron sources.
Leaderless mRNAs Bind 70S Ribosomes More Strongly than 30S Ribosomal Subunits in Escherichia coli. Sean M. O'Donnell, 2002.By primer extension inhibition assays, 70S ribosomes bound with higher affinity, or stability, than did 30S subunits to leaderless mRNAs containing AUG or GUG start codons . Addition of translation initiation factors affected ribosome binding to leaderless mRNAs . Our results suggest that translation of leaderless mRNAs might initiate through a pathway involving 70S ribosomes or 30S subunits lacking IF3 . Crystal Structure of the SarS Protein from Staphylococcus aureus. Ronggui Li, 2003.The expression of virulence determinants in Staphylococcus aureus is controlled by global regulatory loci (e.g., sarA and agr) . One of these determinants, protein A (spa), is activated by sarS, which encodes a 250-residue DNA-binding protein . Genetic analysis indicated that the agr locus likely mediates spa repression by suppressing the transcription of sarS . Contrary to SarA and SarR, which require homodimer formation for proper function, SarS is unusual within the SarA protein family in that it contains two homologous halves, with each half sharing sequence similarity to SarA and SarR . Here we report the 2.2 Å resolution X-ray crystal structure of the SarS protein . SarS has folds similar to those of SarR and, quite plausibly, the native SarA structure . Two typical winged-helix DNA-binding domains are connected by a well-ordered loop . The interactions between the two domains are extensive and conserved . The putative DNA-binding surface is highly positively charged . In contrast, negatively charged patches are located opposite to the DNA-binding surface . Furthermore, sequence alignment and structural comparison revealed that MarR has folds similar to those of SarR and SarS . Members of the MarR protein family have previously been implicated in the negative regulation of an efflux pump involved in multiple antibiotic resistance in many gram-negative species . We propose that MarR also belongs to the winged-helix protein family and has a similar mode of DNA binding as SarR and SarS and possibly the entire SarA protein family member . Based on the structural differences of SarR, SarS, and MarR, we further classified these winged-helix proteins to three subfamilies, SarA, SarS, and MarR . Finally, a possible transcription regulation mechanism is proposed .
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