http://hdl.handle.net/2328/25997 2013-05-20T05:34:41Z http://hdl.handle.net/2328/26329 Title: Ascorbate metabolism and the developmental demand for tartaric and oxalic acids in ripening grape berries Authors: Melino, Vanessa Jane; Soole, Kathleen Lydia; Ford, Christopher M Abstract: We demonstrate strong developmental regulation of ascorbic acid (Asc) biosynthetic, recycling and catabolic genes in grape berries. Integration of the transcript, radiotracer and metabolite data demonstrates that Asc and tartaric acid (TA) metabolism are developmentally regulated in grapevines; resulting in low accumulated levels of the biosynthetic intermediate Asc, and high accumulated levels of the metabolic end-product TA. 2009-01-01T00:00:00Z http://hdl.handle.net/2328/26251 Title: Brain organization and retinal pathways in the sleepy lizard, Tiliqua rugosa Authors: Mayner, Lidia; Sanderson, Kenneth James; Bull, Christopher Michael Abstract: Brain structure and retinal pathways to the brain of the sleepy lizard Tiliqua rugosa were described, with this species identifiable as a type II lizard according to brain organisation. The retinal pathway appeared entirely crossed to the opposite side of the brain with termination of retinal fibres observed in the optic thalamus, pretectum, tectum and brainstem tegmentum. 2009-01-01T00:00:00Z http://hdl.handle.net/2328/26043 Title: Staphyloccal multidrug efflux protein QacA Authors: Brown, Melissa Hackett; Skurray, Ronald Anthony Abstract: The QacA multidrug exporter from Staphylococcus aureus mediates resistance to a wide array of monovalent or divalent cationic, lipophilic, antimicrobial compounds. QacA provides resistance to these various compounds via a proton motive forcedependent antiport mechanism that conforms to classical Michaelis-Menten kinetics. Fluorescent transport analyses have demonstrated that this QacA:substrate interaction occurs with high affinity and competition studies have shown that QacAmediated ethidium export is competitively inhibited by other monovalent cations, and non-competitively inhibited by divalent cations, suggesting that monovalent and divalent cations bind at distinct sites on the QacA protein. The closely related export protein QacB, mediates lower levels of resistance to divalent cations, and lacks a high affinity-binding site for divalent cations. The cell membrane has been identified as the origin of QacA-mediated efflux; substrates are bound and expelled from within this hydrophobic environment. Regulation of qacA expression is achieved via the trans-acting repressor protein, QacR. QacR belongs to the TetR family of transcriptional repressor proteins, which all possess a helix-turn-helix DNA-binding domain at their N-terminal ends, and have highly divergent C-termini postulated to be involved in the binding of inducing compounds. QacR specifically binds to an inverted repeat, IR1, which has been identified as the qacA operator region, and overlaps the identified promoter sequence for qacA. QacR, like the multidrug export protein whose expression it regulates, has been shown to interact directly with a number of structurally-dissimilar compounds. 2001-01-01T00:00:00Z http://hdl.handle.net/2328/26017 Title: The staphylococcal QacR multidrug regulator binds a correctly spaced operator as a pair of dimers Authors: Grkovic, Steve; Brown, Melissa Hackett; Schumacher, Maria A; Brennan, Richard G; Skurray, Ronald Anthony Abstract: Expression of the Staphylococcus aureus plasmid-encoded QacA multidrug transporter is regulated by the divergently encoded QacR repressor protein. To circumvent the formation of disulfide-bonded degradation products, site-directed mutagenesis to replace the two cysteine residues in wild-type QacR was undertaken. Analysis of a resultant cysteineless QacR derivative indicated that it retained full DNA-binding activities in vivo and in vitro and continued to be fully proficient for the mediation of induction of qacA expression in response to a range of structurally dissimilar multidrug transporter substrates. The cysteineless QacR protein was used in cross-linking and dynamic light-scattering experiments to show that its native form was a dimer, whereas gel filtration indicated that four QacR molecules bound per DNA operator site. The addition of inducing compounds led to the dissociation of the four operator-bound QacR molecules from the DNA as dimers. Binding of QacR dimers to DNA was found to be dependent on the correct spacing of the operator half-sites. A revised model proposed for the regulation of qacA expression by QacR features the unusual characteristic of one dimer of the regulatory protein binding to each operator half-site by a process that does not appear to require the prior self-assembly of QacR into tetramers. 2001-01-01T00:00:00Z