OxyFile #220

Mutagenic activity and specificity of hydrogen peroxide 
in the ad-3 forward-mutation test in two-component heterokaryons 
of Neurospora crassa.


Author:  Han JS

Source:  Mutat Res 1997 Mar 21; 374(2):169-84

Abstract:  

In the ad-3 forward-mutation test, hydrogen peroxide was 
at best a weak mutagen in nongrowing conidia from a DNA 
repair-proficient heterokaryon (H-12, uvs-2+/uvs-2+) but 
was a moderate mutagen in nongrowing conidia from a DNA-repair-
deficient heterokaryon (H-59, uvs-2/uvs-2) over a narrow range of 
high concentrations. H-59 also was more sensitive than 
H-12 to the killing activity of hydrogen peroxide at high 
concentrations. Thus, a DNA-repair pathway, of which the 
gene product of the uvs-2+ allele is a part, appears to 
be involved in the repair of hydrogen peroxide-induced 
DNA lesions at low survival in these strains. There was 
slightly, but significantly, more killing by hydrogen peroxide 
of nongrowing conidia from H-12 and H-59 in the presence 
of O2 than in the absence of O2 (presence of N2). Thus, 
the killing activity of hydrogen peroxide was enhanced 
by O2. The Mutational Spectra of hydrogen peroxide-induced 
ad-3 mutants shows that hydrogen peroxide induced mainly 
gene/point mutations but also some multilocus deletion 
mutations in H-12 and H-59. Multiple-locus mutations occurred 
only in H-59, but the frequency was very low. The frequencies 
of the 3 kinds of intracistronic complementation pattern 
among ad-3BR mutants (gene/point mutations) suggest that 
hydrogen peroxide induced both base-pair substitutions 
and frameshift mutations in both strains.