DNA profiling and the law in South Africa

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Abstract

DNA evidence is currently at the forefront of the arsenal of evidence employed in criminal trials. To ensure its optimum use in criminal proceedings, it is imperative that the legal fraternity is properly conversant with the scientific basis and presentation of such evidence, as well as with its potential pitfalls. In an effort to provide the legal profession with a background to this complex and useful type of evidence, this article looks at the biochemical nature of DNA, at DNA profiling and its use in criminal trials, and at the processes of DNA collection and analysis in the Biology Unit of the Forensic Science Laboratory of the South African Police Service. The presentation of DNA evidence in court is then evaluated and the future of DNA evidence, including legislative reform, and the creation of a DNA database are discussed.

Translated abstract

DNA-getuienis is tans van wesenlike belang in die arsenaal van getuienis wat in strafsake gebruik word. Ten einde die optimale gebruik van DNA-getuienis in strafregtelike verrigtinge te verseker, is dit noodsaaklik dat regslui met die wetenskaplike basis en die aanbieding van sodanige getuienis vertroud moet wees, sowel as die moontlike slaggate daarvan. In 'n poging om die regsprofessie met agtergrond van hierdie komplekse en bruikbare tipe getuienis te voorsien, word daar in hierdie artikel na die bio-chemiese aard van DNA, DNA profilering en die aanwending daarvan in strafsake, die versamelingsproses van DNA en ontleding in die Biologie Eenheid van die Forensiese Wetenskap Laboratorium van die Suid-Afrikaanse Polisiediens gekyk. Die aanbieding van DNA-getuienis in die howe word ge-evalueer en die toekoms van DNA-getuienis, insluitende wetgewende hervorming, asook die daarstelling van 'n DNA-databasis, word bespreek.

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Inhibitory DNA ligands to platelet-derived growth factor B-chain.

L Green, D. Jellinek, R Jenison … (1996)

We have identified a group of DNA molecules that bind to platelet-derived growth factor (PDGF)-AB with subnanomolar affinity from a randomized DNA library using in vitro selection. Individual ligands cloned from the affinity-enriched pool bind to PDGF-AB and PDGF-BB with comparably high affinity (Kd approximately 10(-10) M) and to PDGF-AA with lower affinity (> 10(-8) M), indicating specific recognition of the PDGF B-chain in the context of the hetero- or homodimer. The consensus secondary structure motif for most of the high-affinity ligands is a three-way helix junction with a three-nucleotide loop at the branch point. Photo-cross-linking experiments with 5-iodo-2'-deoxyuridine-substituted ligands establish a point contact between a thymidine nucleotide in the helix junction loop region and phenylalanine 84 of the PDGF-B chain. Representative minimal DNA ligands inhibit the binding of 125I-PDGF-BB but not of 125I-PDGF-AA to PDGF alpha- or beta-receptors expressed in porcine aortic endothelial (PAE) cells in a concentration-dependent manner with half-maximal effects of approximately 1 nM. The same ligands also exhibit a similar inhibitory effect on PDGF-BB-dependent [3H]thymidine incorporation in PAE cells expressing the PDGF beta-receptors. These DNA ligands represent a novel class of specific and potent antagonists of PDGF-BB and, by inference, PDGF-AB.

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Intramolecular N-Glycan/Polypeptide Interactions Observed at Multiple N-Glycan Remodeling Steps through [13C,15N]-N-Acetylglucosamine Labeling of Immunoglobulin G1

Adam W. Barb (2014)

Asparagine-linked (N) glycosylation is a common eukaryotic protein modification that affects protein folding, function, and stability through intramolecular interactions between N-glycan and polypeptide residues. Attempts to characterize the structure–activity relationship of each N-glycan are hindered by inherent properties of the glycoprotein, including glycan conformational and compositional heterogeneity. These limitations can be addressed by using a combination of nuclear magnetic resonance techniques following enzymatic glycan remodeling to simultaneously generate homogeneous glycoforms. However, widely applicable methods do not yet exist. To address this technological gap, immature glycoforms of the immunoglobulin G1 fragment crystallizable (Fc) were isolated in a homogeneous state and enzymatically remodeled with [13C,15N]-N-acetylglucosamine (GlcNAc). UDP-[13C,15N]GlcNAc was synthesized enzymatically in a one-pot reaction from [13C]glucose and [15N-amido]glutamine. Modifying Fc with recombinantly expressed glycosyltransferases (Gnt1 and Gnt2) and UDP-[13C,15N]GlcNAc resulted in complete glycoform conversion as judged by mass spectrometry. Two-dimensional heteronuclear single-quantum coherence spectra of the Gnt1 product, containing a single [13C,15N]GlcNAc residue on each N-glycan, showed that the N-glycan is stabilized through interactions with polypeptide residues. Similar spectra of homogeneous glycoforms, halted at different points along the N-glycan remodeling pathway, revealed the presence of an increased level of interaction between the N-glycan and polypeptide at each step, including mannose trimming, as the N-glycan was converted to a complex-type, biantennary form. Thus, conformational restriction increases as Fc N-glycan maturation proceeds. Gnt1 and Gnt2 catalyze fundamental reactions in the synthesis of every glycoprotein with a complex-type N-glycan; thus, the strategies presented herein can be applied to a broad range of glycoprotein studies.