QUANTITATIVE AND QUALITATIVE COMPARISONS OF SPONTANEOUS AND RADIATION-INDUCED SPECIFIC-LOCUS MUTATION IN THE AD-3 REGION OF HETEROKARYON-12OF NEUROSPORA-CRASSA
Fj. Deserres et Bb. Webber, QUANTITATIVE AND QUALITATIVE COMPARISONS OF SPONTANEOUS AND RADIATION-INDUCED SPECIFIC-LOCUS MUTATION IN THE AD-3 REGION OF HETEROKARYON-12OF NEUROSPORA-CRASSA, Mutation research, 375(1), 1997, pp. 37-52
The data from forward-mutation experiments to obtain specific-locus mu
tations at two closely linked loci in the adenine-3 (ad-3) region of h
eterokaryon 12 (H-12) of Neurospora crassa have been used to determine
the relative frequencies and mutational spectra of ad-3 mutants occur
ring spontaneously and those induced by 7 different radiation treatmen
ts. Previous studies have demonstrated that specific-locus mutants at
these two loci result from 5 major genotypic classes, namely two class
es of gene/point mutations (ad-3A(R) and ad-3B(R)), and 3 classes of m
ultilocus deletion mutations ([ad-3A](IR), [ad-3B](IR) and [ad-3A ad-3
B](IR)). Two different approaches were used to compare spontaneous mut
ation in the ad-3 region with that induced by 7 different radiation tr
eatments (UV, P-32, 447 MeV protons, Sr-85, 250 kVp X-rays, 39 MeV hel
ium ions, and 101 MeV carbon ions). These comparisons included (2)(chi
)-tests on the numbers of ad-3 mutants resulting in the following two
sets of ratios: (1) gene/point mutations and multilocus deletion mutat
ions; and (2) complementing and non-complementing ad-3B(R) mutants. Co
mbination of the data from these two methods of comparison has demonst
rated that each of the 7 radiation treatments induced a spectrum of ad
-3 mutants that is statistically different from the spontaneous spectr
um. In addition, these same two methods of comparison have been used t
o compare the mutagenic effects of each of the 7 radiation treatments
with each other. Combination of the data from these two methods of com
parison demonstrated that the majority of radiation-induced specific-l
ocus mutations: (90.5% (19/21 of the pairwise combinations)) are quali
tatively different from each other. We conclude that the mechanisms by
which various radiations modify DNA tend to exhibit fundamental diffe
rences from each other and from the processes involved in spontaneous
mutation.