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Biomedical subjects

K L Yielding

Publications and source records attributed to K L Yielding.

At least 73 records · Page 4Linked to original sources
PubMed1977

Synthesis, separation and characterization of the mono- and diazide analogs of ethidium bromide.

Ethidium bromide is used to characterize nucleic acid secondary and tertiary structural properties and the biological consequences of drug interactions. The mono- and diazido analogs of ethidium have proven valuable as photoaffinity probes in chemical and biological studies on nucleic acids, since they render the ethidium-nucleic acid interaction covalent. Although both of these compounds have been synthesized previously, the published synthesis procedure for the monoazide is inadeqlate since a major portion of the product has been identified as the diazide analog. This lack of purity severely limits the usefulness for nucleic acid research. The procedure presented here for the synthesis, separation, purification and crystallization of these analogs should provide the quantities and quality of these important reagents needed to perform a variety of chemical and biological experiments.

Azides↗
PubMed1977

Induction of respiratory deficient mutants in Saccharomyces cerevisiae by mono- and diazido analogs of ethidium.

Mono- and diazido analogs of ethidium when photolyzed with yeast cells were highly effective in inducing respiratory deficient (RD) mutants. The monoazide was more mutagenic, though slightly less photosensitive, and under the concentrations and conditions used, both required photolysis to be significantly mutagenic. Ethidium bromide (EB) competed with either its mono- or diazide analog for RD induction when applied before, but not after, the photolysis step. This suggested that the initial mutagenic binding sites for azides were identical with those of EB. There was no self-rescue or recovery in azide mutagenesis in contrast to EB. Furthermore, recovery from azide mutagenesis could not be provoked by EB. This confirmed a simple competition between binding of EB and its azide analogs to account for the prevention by EB of the azide induced mutations.

Binding Sites↗
PubMed1976

A protective effect of caffeine on the ethidium induced petite mutation in yeast.

A prerequisite for petite induction by ethidium bromide (EB) is an initial covalent attachment of the drug to cytoplasmic DNA. This DNA modification is thought to initiate repair processes. The repair inhibitor, caffeine, provided a protective effect against the ethidium induced petite mutation at caffeine concentrations known to inhibit the repair of UV damage in cytoplasmic DNA (Fig. 1). Mitochondrial DNA isolated from yeast exposed to EB in vivo was not as degraded in the presence of both drugs as with EB alone (Fig. 2).

Caffeine↗
PubMed1976

Production of frameshift mutations in Salmonella by a light sensitive azide analog of ethidium.

Frameshift mutations have been produced in specific repair-negative Salmonella tester strains by photoaffinity labeling technique using ethidium azide. Reversions requiring a +1 addition or a -2 deletion were specially sensitive. Mutagenesis was reduced by the simultaneous addition of non-mutagenic ethidium bromide, and was prevented by photolysis of the azide prior to culture addition. Identical tester strains active in DNA excision repaire were not mutagenized by the azide. These results are consistent with the interpretation that photolysis of the bound ethidium analog converts the drug from its noncovalent mode of binding (presumably intercalation) to a covalent complex with consequent production of frameshift mutations. Such photoaffinity labeling by drugs which bind to DNA not only confirms the importance of covalent drug attachment for frameshift mutagenesis, but also provides powerful techniques for studying the molecular deatils of a variety of genetic mechanisms.

Azides↗
PubMed1976

Inhibition by nalidixic acid of post-uv survival of Escherichia coli.

Nalidixate inhibited the post-uv survival of E. coli B. TAU-bar and Ts-7, but not Bs-1 or B/r when included in the plating medium. Removal of the drug sensitivity by photoreactivation was consistent with pyrimidine dimers as the target for the effect. Nalidixate did not inhibit liquid-holding recovery from uv when included in the holding medium, but survival was inhibited if the drug was in the subsequent plating medium. In fact, there was an actual increase in the number of nonsurvivors due to the drug following a period of holding.

DNA Repair↗
PubMed1975

Evidence for the dark repair of ultraviolet damage in Saccharomyces cerevisiae mitochondrial DNA.

Evidence for the dark repair of ultraviolet damage to yeast mitochondrial DNA has been observed. The ultraviolet dose necessary to inflict significant damage to both nuclear and mitochondrial DNA was determined. Cell survival at large doses of ultraviolet light was observed after immediate and delayed plating of yeast onto 1% pyruvate and 1% glucose media. In the highly lethal dose ranges of irradiation an increase in the number of normal colonies appeared after a period of liquid holding and delayed plating. This increase, demonstrated separately on 1% glucose and 1% pyruvate media suggested that the repair of both mitochondrial and nuclear DNA had occurred. After low doses of ultraviolet light an actual decrease in the number of petite survivors was seen after delayed plating, even though the total number of survivors increased. When a known repair inhibitor, caffeine, was added to the liquid holding buffer prior to the delayed plating of yeast, a marked decrease in the number of petites did not occur after delayed plating. Therefore, the decrease in the number of petite survivors after delayed plating following low doses of ultraviolet light is attributed to the repair of yeast mitochondrial DNA.

DNA Repair↗