Polynucleotide Celluloses as Solid State Primers and Templates for Polymerases

The Origin of Left-Handed Poly[d(G-C)]

The discovery of a reversible transition in the helical sense of a double-helical DNA was initiated by the first synthesis in 1967 of the alternating sequence poly[d(G-C)]. In 1968, exposure to high salt concentration led to a cooperative isomerization of the double helix manifested by an inversion in the CD spectrum in the 240-310 nm range and in an altered absorption spectrum. The tentative interpretation, reported in 1970 and then in detailed form in a 1972 publication by Pohl and Jovin, was that the conventional right-handed B-DNA structure (R) of poly[d(G-C)] transforms at high salt concentration into a novel, alternative left-handed (L) conformation. The historical course of this development and its aftermath, culminating in the first crystal structure of left-handed Z-DNA in 1979, is described in detail. The research conducted by Pohl and Jovin after 1979 is summarized, ending with an assessment of "unfinished business": condensed Z*-DNA; topoisomerase IIα (TOP2A) as an allosteric ZBP (Z-DNA-binding protein); B-Z transitions of phosphorothioate-modified DNAs; and parallel-stranded poly[d(G-A)], a double helix with high stability under physiological conditions and potentially also left-handed.

Cyanogen bromide-activated coupling: DNA catalytic chromatography purification of EcoRI endonuclease

A method to purify enzymes utilizing their specific biological affinity and catalytic specificity is described. For this chromatographic technique, an enzyme binds immobilized substrate coupled to a column in the absence of a cofactor required for catalysis but permissive for substrate binding. After washing, the missing cofactor is added to the column mobile phase, and the enzyme converts substrate into product and elutes from the column. A single-step purification of EcoRI endonuclease using a sequence-specific DNA column (containing the GAATTC motif coupled to cyanogen bromide-activated Sepharose 4B) binds EcoRI in the absence of Mg2+ and elutes when Mg2+ is applied in a highly purified state. Although the method described is specific for EcoRI, it can be readily modified for the purification of DNA polymerases and other enzymes. Furthermore, many of the same materials are also used for transcription factor purification. This protocol can be completed within 4-6 d.

Mechanism of action of penicillamine in the treatment of avian muscular dystrophy

Penicillamine, a cysteine analog with a reduced sulfhydryl group, has been used in this laboratory for the treatment of hereditary avian dystrophy. The drug delays the onset of symptoms and alleviates the debilitating aspects of the disease. To study the mechanism of drug action, the effects of penicillamine on white and red muscles of dystrophic chickens were examined with regard to the specific activities of the soluble enzymes glyceraldehyde-3-phosphate dehydrogenase, acetylphosphatase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glutathione reductase, glutathione preoxidase, superoxide dismutase, and catalase. The sulfhydryl contents of the soluble proteins and the concentration of myoglobin were also determined. In white dystrophic muscle (pectoral), there were large alterations in the various enzymatic activities compared to normal levels. In the DISCUSSION, these changes are related to the pathogenesis of the disease and to the adaptive response for protection of the severely affected fast fibers. Red dystrophic muscles (thigh) were minimally involved, in accordance with the known sparing action of the slow fiber type. The results suggested that the disease process in dystrophic muscle may be due to oxidation of the essential sulfhydryl groups of proteins. Penicillamine may produce therapeutic effects by altering the intracellular redox status, thereby promoting better regulation of enzymatic activity, membrane stability, and improved muscle function.

Covalent attachment of DNA to agarose. Improved synthesis and use in affinity chromatography

DNA has been covalently linked to insoluble matrices of agarose (Sepharose) in high yield using cyanogen bromide activation. Both double-stranded and single-stranded DNA have been coupled with yields up to 225 nmol/mg dry weight Sepharose or 3-8 mumol nucleotide phosphate/ml bed volume. The DNA-Sepharose has been used for (a) the affinity chromatography of various enzymes (Escherichia coli DNA polymerase I and RNA polymerase) from crude extracts or after initial purification steps, resulting in high yields and degrees of purification, and for (b) nucleic acid hybridization. The DNA-Sepharose is stable to high temperature, prolonged storage, and in the case of single-stranded DNA, can be washed with NaOH to destroy nuclease activity and to release any digested oligonucleotides or mononucleotides.