An SV40-based s
huttle vector system was used to identify t
he types of mutational c
hanges and t
he sites of mutation wit
hin t
he
supF DNA sequence generated by t
he four stereoisomers of benzo[
c]p
henant
hrene 3,4-di
hydrodiol 1,2-epoxide (B[
c]P
hDE), by racemic mixtures of bay or fjord region di
hydrodiol epoxides (DE) of 5-met
hylc
hrysene, of 5,6-dimet
hylc
hrysene, of benzo[
g]c
hrysene and of 7-met
hylbenz[
a]ant
hracene and by two direct acting polycyclic aromatic
hydrocarbon carcinogens, 7-bromomet
hylbenz[
a]ant
hracene (7-BrMeBA) and 7-bromomet
hyl-12-met
hylbenz[
a]ant
hracene (7-BrMe-12-MeBA). T
he results of t
hese studies demonstrated t
hat t
he predominant type of mutation induced by t
hese compounds is t
he base substitution. T
he c
hemical preference for reaction at deoxyadenosine (dAdo) or deoxyguanosine (dGuo) residues in DNA, w
hic
h is in general correlated wit
h t
he spatial structure (planar or non-planar) of t
he reactive polycyclic aromatic
hydrocarbon, is reflected in t
he preference for mutation at A
![](/images/glyp<font)
hs/BL9.GIF>T or G
![](/images/glyp<font)
hs/BL9.GIF>C pairs. In addition, if t
he ability to react wit
h DNA in vivo is taken into account, t
he relative mutagenic potencies of t
he B[
c]P
hDE stereoisomers are consistent wit
h t
he
hig
her tumorigenic activity associated wit
h non-planar polycyclic aromatic
hydrocarbons and t
heir extensive reaction wit
h dAdo residues in DNA. Comparison of t
he types of mutations generated by polycyclic aromatic
hydrocarbons and ot
her bulky carcinogens in t
his s
huttle vector system suggests t
hat all bulky lesions may be processed by a similar mec
hanism related to t
hat involved in replication past apurinic sites. However, inspection of t
he distribution of mutations over t
he target gene induced by t
he different compounds demonstrated t
hat individual polycyclic aromatic
hydrocarbons induce unique patterns of mutational
hotspots wit
hin t
he target gene. A polymerase arrest assay was used to determine t
he sequence specificity of t
he interaction of reactive polycyclic aromatic
hydrocarbons wit
h t
he s
huttle vector DNA. T
he results of t
hese assays revealed a divergence between mutational
hotspots and polymerase arrest sites for all compounds investigated, i.e., sites of mutational
hotspots do not correspond to sites w
here
hig
h levels of adduct formation occur, and suggested t
hat some association between specific adducts and sequence context may be required to constitute a premutagenic lesion. A site-specific mutagenesis system employing a single-stranded vector (M13mp7L2) was used to investigate t
he mutational events a single benzo[
a]pyrene or benzo[
c]p
henant
hrene di
hydrodiol epoxide&ndas
h;DNA adduct elicits wit
hin specific sequence contexts. T
hese studies s
howed t
hat sequence context can cause striking differences in mutagenic frequencies for given adducts. In addition, t
hese sequence context effects do not originate only from nucleotides immediately adjacent to t
he adduct, but are also modulated by more distal nucleotides. T
he implications of t
hese results for mec
hanisms of polycyclic aromatic
hydrocarbon-induced mutagenesis and carcinogenesis are discussed.