title: Molecular and cellular characterisation of the zinc uptake (Znu) system of Nostoc punctiforme.
abstract: Metal homoeostasis in cyanobacteria is based on uptake and export systems that are controlled by their own regulators. This study characterises the zinc uptake (Znu) system in Nostoc punctiforme. The system was found to comprise of three subunits in an ACB operon: a Zn(2+)-binding protein (ZnuA18), a transmembrane domain (ZnuB) and an ATPase (ZnuC). These proteins are encoded within the znu operon regulated by a zinc uptake transcription repressor (Zur). Interestingly, a second Zn(2+)-binding protein (ZnuA08) was also identified at a distal genomic location. Interactions between components of the ZnuACB system were investigated using knockouts of the individual genes. The znuA08(-), znuA18(-), znuB(-) and znuC(-) mutants displayed overall reduced znuACB transcript levels, suggesting that all system components are required for normal expression of znu genes. Zinc uptake assays in the Zn(2+)-binding protein mutant strains showed that the disruption of znuA18 had a greater negative effect on zinc uptake than disruption of znuA08. Complementation studies in Escherichia coli indicated that both znuA08 and znuA18 were able to restore zinc uptake in a znuA(-) mutant, with znuA18 permitting the highest zinc uptake rate. The N. punctiforme zur was also able to complement the E. coli zur(-) mutant.
authors.affiliation: Centre for Cellular and Molecular Biology, School of Life and Environmental Sciences, Deakin University, Burwood, Vic., Australia.
authors.forename: Lee
authors.initials: L
authors.lastname: Hudek
authors.forename: Leanne A
authors.initials: LA
authors.lastname: Pearson
authors.forename: Agnes
authors.initials: A
authors.lastname: Michalczyk
authors.forename: Brett A
authors.initials: BA
authors.lastname: Neilan
authors.forename: M Leigh
authors.initials: ML
authors.lastname: Ackland
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D000251:Adenosine Triphosphatases / Q000235:genetics; D027682:Cation Transport Proteins / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D017136:Ion Transport; D009154:Mutation; D046937:Nostoc / Q000235:genetics* / Q000378:metabolism*; D009876:Operon; D015032:Zinc / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; C488663:ZnuA protein, E coli; C546032:ZnuB protein, E coli; C571000:ZnuC protein, E coli; D000251:Adenosine Triphosphatases; D015032:Zinc
keywords: Nostoc punctiforme; heavy metals; metal transporters; zinc