No abstract

The ability of relatively stable Cr(V) and Cr(IV) complexes with 2-hydroxycarboxylato ligands [2-ethyl-2-hydroxybutanoate(2-) = ehba; (1R,3R,4R,5R)-1,3,4,5-tetrahydroxycyclohexanecarboxylate(2-) = quinate = qa] to induce single-strand breaks in plasmid DNA has been studied under a wide range of reaction conditions. The Cr(V) complex, Na[CrVO(ehba)2], causes substantial DNA cleavage at pH 4.0-8.0 [[Cr(V)]0 = 0.010-0.75 mM, phosphate buffer, and 37 degrees C]. The DNA cleavage is inhibited by the presence of excess ligand, by exclusion of O2, or by addition of organic compounds, such as alcohols, carboxylic acids, or DMSO, but it is not affected by traces of catalytic metals [Fe(III) or Cu(II)] or by addition of catalase. The Cr(IV)-qa complexes, unlike the Cr(V) complexes, are able to cleave DNA in the presence of the ligand in a large excess [[Cr(IV)]0 = 0.50 mM, [qa] = 20-100 mM, pH 3.5-6.0, and 37 degrees C]. This is the first direct evidence for DNA cleavage induced by well-characterized Cr(IV) complexes. The proposed mechanism for DNA cleavage includes the following: (i) partial aquation of the bis-chelated Cr(V) and -(IV) complexes with the formation of reactive monochelated forms, (ii) binding of the Cr(V) and -(IV) monochelates to the phosphate backbone of DNA, (iii) one- or two-electron oxidations at the deoxyribose moieties of DNA by Cr(V) and -(IV), and (iv) cleavage of the resulting DNA radicals or cations with or without participation of O2. The patterns of DNA damage by Cr(V) and -(IV) can include strand breaks, generation of abasic sites, and the formation of Cr(III)-DNA complexes.

No abstract

The capacity of our gut microbial communities to maintain a stable and balanced state, termed 'resilience', in spite of perturbations is vital to our achieving and maintaining optimal health. A loss of microbial resilience is observed in a number of diseases including obesity, diabetes and metabolic syndrome. There are large gaps in our understanding of why an individual's co-evolved microflora consortium fail to develop resilience thereby establishing a trajectory towards poor metabolic health. This review examines the connections between the developing gut microbiota and intestinal barrier function in the neonate, infant and during the first years of life. We propose that the effects of early life events on the gut microflora and permeability, whilst it is in a dynamic and vulnerable state, are fundamental in shaping the microbial consortia's resilience and that it is the maintenance of resilience that is pivotal for metabolic health throughout life. We review the literature supporting this concept suggesting new potential research directions aimed at developing a greater understanding of the longitudinal effects of the gut microflora on metabolic health and potential interventions to recalibrate the 'at risk' infant gut microflora in the direction of enhanced metabolic health.

No abstract

No abstract

The hammerhead ribozyme, as engineered by J. Haseloff and W. L. Gerlach [(1988) Nature (London) 334,[585][586][587][588][589][590][591], is an RNA molecule containing two regions of conserved nucleotides, a double helix, called helix H, which connects the two conserved regions, and flanking arms of variable sequence, which hybridize the ribozyme to its specific target. Here we show that this ribozyme may be reduced in size and still retain cleavage activity by replacing helix II with just a few nucleotides that cannot form Watson-Crick base pairs between themselves. Furthermore, the nucleotides replacing heli II and the nucleotides in the flanking arms may be substituted with DNA, and this small, DNA-containing ribozyme is fully as active as the original, full-size ribozyme. Cleavage activity of the minimized ribozyme depends on the number and sequence of the few nucleotides that replace helix II; optimal activity, thus far, is achieved by four or five deoxyribopyrimidines. The minimized ribozyme, or "mimnzyme," is active as a monomer, as shown by its nearly constant activity over a concentration range varying 25,000-fold, by the mobility of the minizyme-substrate complex in nondenaturing polyacrylamide gels as compared with other nucleic acid molecules of known size, and by other observations. These minizymes provide an excellent model system for studying the structure and mechanism of catalytic RNA; they might also be useful in a variety of biological applications.Ribozymes are RNA molecules that can cut or ligate other RNA or DNA molecules in a catalytic fashion (1,2). The hammerhead ribozyme, one of the best-known ribozymes, has been studied extensively in isolated chemical systems (3-7) and used in gene-control studies in living cells (8)(9)(10)(11). The essential features of a hammerhead ribozyme were determined initially by comparing the base sequences (3, 12) of a number of plant virusoids, linear satellite RNAs, and a viroid that can all cut themselves at unique locations (12-14); later they were refined in a comprehensive study of base mutations (15). These essential features are (i) three double helices of any base sequence, which meet at the cleavage site, (ii) the site of cleavage that has a sequence UX, with cleavage occurring on the 3' side of X, and (iii) two stretches of nucleotides of sequence 5'-CUGAZGA and 5'-GAAA, where X and Z are any base except guanine. It is possible to separate these essential features into two parts, a ribozyme and a substrate, in several ways (4, 5). A hammerhead ribozyme as defined by Haseloff and Gerlach (5) is shown in Fig. 1 at the top. This ribozyme contains the two stretches of conserved nucleotides and one of the three double helices (helix II), whereas the substrate forms double helices I and III in combination with the ribozyme. Because the base sequences of helices I and III are not conserved, the ribozyme may be designed to cut a substrate of virtually any sequence.Our primary aim in this work was to minimize the size of a Haseloff-Gerlach ribozym...

No abstract