Mutation as cellular process : a Ciba Foundation symposium / edited by G.E.W. Wolstenholme and Maeve O'Connor.

  • Symposium on Mutation as Cellular Process (1969 : London, England)
Date:
1969
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Mutation as cellular process : a Ciba Foundation symposium / edited by G.E.W. Wolstenholme and Maeve O'Connor. Source: Wellcome Collection.

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    FACTORS THAT MODIFY MUTAGEN SPECIFICITY 57 PHOTOREPAIR Photorepair is the only repair system in fungi for which definite bio¬ chemical evidence exists at present. The enzyme has been extracted from Neurospora conidia and can reactivate u.v.-inactivated transforming principle in vitro (Terry, Kilbey and Branch-Howe, 1967). In earlier experiments Kilbey and de Serres (1967) were able to show that photorepair is apparently unspecific: all classes of u.v.-induced ad-^B mutants were diminished when photorepair was allowed to function. In view of this it was all the more surprising to fmd that in both the K3/17 and the cot strains, photorepair is specific for adenine reversions (Kilbey, 1967). Fig. 4 shows ad У10' survivors 30 40 mos У10^ survivors Fig. 4. Differential photoreactivation of mutation and survival in the cot derivative. PR: photorepair. the two types of mutation plotted versus survival, with and without photorepair. The same dose reduction factor applies to both adenine reversions and survival ; thus the points fall on one curve whether they come from photoreactivated samples or not. Inositol reversions are only slightly responsive to photorepair and, when plotted against survival, points from the light and dark samples fall on different curves. The behaviour of the inositol mutant appears to be unique. Two other inos alleles were tested together with two ad-^A alleles and ten ad-'¡B alleles. All of these were photoreactivated to the same extent as ad-^A 38701 although their u.v. responses differed considerably. The finding that photorepair operated specifically upon adenine rever¬ sions in this system led to a re-examination of the possibility that photo- reactivation, caused by the visible light emitted by our u.v. source, was