Ca. Wijker et Mvm. Lafleur, INFLUENCE OF THE UV-ACTIVATED SOS RESPONSE ON THE GAMMA-RADIATION-INDUCED MUTATION SPECTRUM IN THE LACI GENE, Mutation research. DNA repair, 408(3), 1998, pp. 195-201
Previous studies of our group have shown that intracellular or extrace
llular gamma-irradiation of the lad gene results in different mutation
al spectra. One cause for these differences might be the error-prone S
OS response, which is activated in the intracellular situation by gamm
a-irradiation but not in the extracellular situation. Since UV-radiati
on is a well-established strong inducer of the SOS response, we used b
acterial host cells, pretreated with UV-light to study the influence o
f the SOS response on the gamma-radiation-induced mutation spectrum in
the lacI gene in the extracellular situation. If the SOS response was
activated, mutations on A:T base pairs and frameshift mutations accou
nted for 16% and 12% of all mutations, respectively, but they were har
dly detected in the absence of an induced SOS response. G:C to T:A tra
nsversions increased from 14% to 24% in the presence of an activated S
OS response. We can therefore conclude from this study, that SOS-induc
tion of host cells by UV-light influences the extracellular mutation s
pectrum in the lad gene, with respect to mutations on A:T base pairs,
G:C to T:A transversions and frameshift mutations. This conclusion is
supported by the fact that the previously obtained intracellular gamma
-radiation-induced mutation spectrum in the lad gene, in which the SOS
response is also involved, shows great similarities with the extracel
lular mutation spectrum in the presence of an activated SOS response i
n this study. (C) 1998 Elsevier Science B.V. All rights reserved.