Mutagenesis

ttYDROXYLAMINE AS A MUTAGENIC AGENT FOR NEUROSPORA
CRA SSA
H. V. MALLING
Biolog 3' Division, Oak Ridge National Laboralor),, Oak l?idge, Tenn. (U.S.d.)
(Received June 2ist, I000)
SUMMARY
Themutagenicity of hydroxylamine (HA) has been tested in 8 different adeninerequiring
mutants (ad-3B) of Neuro@ora crassa: 4 mutants of this tester set revert
after treatment with nitrous acid and ethylmethanesulfonate indicating that they
revert by a base-pair substitution, 2 mutants revert only after treatment with ICR-
17o indicating that they revert by a base-pair insertion or deletion, and 2mutants
revert only spontaneously. HA induced reversions in 3 of the 4 mutants which revert
by base-pair substitution and in none of the others. The specificity of the action of
HA on the mutantsin the present tester set is consistent with the hypothesis that the
predominant class of genetic alterations induced by HA in Neuro@ora is base-pair
transitions from guanine-cytosine to adeninethymine. Furthernlore, it was found
that the reversion frequency after HA treatment increases in proportion to the
square of the treatment time.
INTROI) UCTION
HA induces base-pair substitutions inphage and the type of the genetic alterations
is preferentially 9 from GC to AT. The chemical reaction between HA and DNA
has been analyzed by FREESE et al. 8 who found that HA reacts only withcytosine
and HMC. Treatment of RNA with HA alters both uracil and cytosine; at pH 6.1 the
reaction is much faster with cytosine than with uracil, whereas at higher pH the
relationship is reversedlL HAhas been shown to induce chromosonml damage in
mammalian cells 1", but no previous attempt has been successful in identifying the
genetic alteration(s) induced by HA in eukaryotes at the molecularlevel. The characterization
of HA-induced mutations in Neurospora is particularly important because
it may be as specific in eukaryotes as in phage in producing mutations by base-pair
substitutions...