Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.9 (enterokinase)
 675 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A chromosomally encoded znt operon of Staphylococcus aureus consists of two consecutive putative genes designated zntR and zntA. The zntA gene encodes a transmembrane protein that facilitates extrusion of Zn2+ and Co2+, whereas the zntR gene encodes a putative regulatory protein that controls the expression of the znt operon. The zntR gene was amplified using the polymerase chain reaction, cloned into Escherichia coli for overexpression as His-tagged ZntR and purified by Ni2+-affinity column. His-tag-free ZntR was purified to near homogeneity after digestion with enterokinase. Electrophoretic mobility shift assays (EMSAs) indicated that the ZntR bound to a fragment of DNA corresponding to the chromosomal znt promoter region with an affinity of about 8.0 x 10-12 M. The addition of 25 microM Zn2+ or Co2+ in the binding reaction completely or significantly inhibited association of ZntR with the znt promoter. DNase I footprinting assays identified a ZntR binding site encompassing 49 nucleotides in the znt promoter region that contained repeated TGAA sequences. These sequences have been proposed to be the binding sites for SmtB, a metallorepressor protein from the cyanobacterium Synechococcus, to its corresponding operator/promoter. In vitro transcription assays, using S. aureus RNA polymerase, revealed that ZntR represses transcription from the znt promoter in a concentration-dependent fashion. The EMSAs, DNase I footprinting and in vitro transcription assays indicate that ZntR is a trans-acting repressor protein that binds to the znt promoter region and regulates its own transcription together with that of zntA.
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PMID:ZntR is an autoregulatory protein and negatively regulates the chromosomal zinc resistance operon znt of Staphylococcus aureus. 1041 36

Iron is an essential nutrient for the survival and pathogenesis of bacteria, but relatively little is known regarding its transport and regulation in staphylococci. Based on the known sequences of ferric-uptake regulatory (fur) genes from several Gram-positive and Gram-negative bacteria, a fragment containing the fur homologue was cloned from a genomic library of Staphylococcus aureus RN450. Nucleotide sequence analysis of this fragment revealed the presence of a 447 bp ORF that encodes a putative 149 aa polypeptide with an apparent molecular mass of 17 kDa. A putative ferrichrome-uptake (fhu) operon, containing the conserved Fur-binding sequences (Fur box) in the promoter region, was also cloned from the same S. aureus library. To characterize the impact of Fur on the fhu operon, fur was cloned, overexpressed as a His-tagged protein and purified by Ni2+-affinity column chromatography. The recombinant protein was digested with enterokinase to remove the His tag. Electrophoretic mobility-shift assays indicated that Fur binds to the promoter region of the fhu operon in the presence of divalent cations. Fur also interacted with the promoter region of the recently reported sir operon that has been proposed to constitute a siderophore-transport system in S. aureus. The DNase I-protection assay revealed that Fur specifically binds to the Fur box located in the promoter region of the fhu operon. The primer-extension reaction indicated that the transcription-start site of the fhu operon was located inside the Fur box. S. aureus fur partially complemented a fur- mutation in Bacillus subtilis. The data suggest that Fur regulates iron-transport processes in S. aureus.
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PMID:Molecular characterization of the ferric-uptake regulator, fur, from Staphylococcus aureus. 1074 69