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S J MacFarlane

Publications and source records attributed to S J MacFarlane.

At least 19 recordsLinked to original sources
PubMed1987

Molecular evidence for cleavage of intradimer phosphodiester linkage as a novel step in excision repair of cyclobutyl pyrimidine photodimers in cultured human cells.

A re-analysis of the metabolic fate of ultraviolet light (u.v.)-induced cyclobutyl pyrimidine dimers in the DNA of dermal fibroblasts from patients with different genetic forms of xeroderma pigmentosum (XP), a rare cancer-prone skin disorder, has provided new insight into the mode of dimer repair in normal human cells. When DNA isolated from post-u.v. incubated cultures was subjected to enzymic photoreactivation (PR) to probe dimer authenticity, single-strand scissions were produced in the damaged DNA of incubated XP group A and D cells, but not in DNA from XP group C cells or normal controls. Since enzymic PR treatment ruptures only the cyclobutane ring, these results suggested that in dimer excision-defective XP group A and D strains, the intradimer phosphodiester bond may have been cleaved without site restoration. Such a cleavage event had not previously been detected; the possibility that this reaction may be an early step in the normal excision-repair process is supported by the observed release of free thymidine (dThd) and its monophosphate (TMP), but not of thymine, upon photochemical reversal of the dimer-containing excision fragments isolated from post-u.v. incubated normal cells. The combined number of dThd and TMP molecules released was equal to approximately equal to 80% of the number of dimers photoreversed; for such release to occur, the dimer must both be at one end of an excised fragment and contain an internal phosphodiester break. Taken together, these data lead us to propose a novel model for dimer repair in human cells in which hydrolysis of the intradimer phosphodiester linkage precedes the concerted action of a generalized 'bulky lesion-repair complex' involving conventional strand incision/lesion excision/repair resynthesis/strand ligation reactions.

Cells, Cultured↗
PubMed1985

Cellular hypersensitivity to chronic gamma-radiation in cultured fibroblasts from ataxia-telangiectasia heterozygotes.

Retrospective studies of cancer incidence in AT families suggest that the major detrimental impact of the AT gene on the health of the general population stems from its disease-predisposing potential in heterozygotes. The absence of a definitive marker for routine identification of such carriers, however, has previously precluded direct validation of this predicted effect of AT heterozygosity. We demonstrate that chronic gamma-ray exposure, because it expands the difference in radiation cytotoxicity between normal and heterozygotic strains compared to acute dose delivery, may point the way to development of a reliable laboratory diagnostic procedure for identification of carriers of a defective AT gene.

Ataxia Telangiectasia↗