H. Kamiya et al., 8-HYDROXYGUANINE (7,8-DIHYDRO-8-OXOGUANINE) IN HOT-SPOTS OF THE C-HA-RAS GENE - EFFECTS OF SEQUENCE CONTEXTS ON MUTATION SPECTRA, Carcinogenesis, 16(4), 1995, pp. 883-889
We previously reported that 8-hydroxyguanine (7,8-dihydro-8-oxoguanine
) at the second position of codon 12 of the c-Ha-ras gene induces many
types of mutations in NIH3T3 cells. In this study we incorporated the
modified base into the first and second positions of codon 12 in the
coding strand and into the first position of codon 61 in the non-codin
g strand of the gene using a new 8-hydroxyguanine phosphoramidite as a
building block during oligonucleotide synthesis. The ras genes with 8
-hydroxyguanine were transfected into NIH3T3 cells and the mutations i
nduced were analyzed. 8-Hydroxyguanine residues at the first positions
of codons 12 and 61 induced mutations to T at the modified sites almo
st exclusively. On the other hand, the DNA lesion at the second positi
on of codon 12 induced a G --> A transition in addition to a G --> T t
ransversion, confirming our previous results. Mutations in 5'-flanking
sites were observed with 8-hydroxyguanine at the second position of c
odon 12 or the first position of codon 61. These results indicate that
8-hydroxyguanine in mammalian cells mainly induces a G --> T transver
sion at the modified site, but that other types of mutations are also
elicited.