Yq. Yong et Lj. Romano, BENZO[A]PYRENE-DNA ADDUCTS INHIBIT THE DNA HELICASE ACTIVITY OF THE BACTERIOPHAGE-T7 GENE-4-PROTEIN, Chemical research in toxicology, 9(1), 1996, pp. 179-187
The gene 4 protein of bacteriophage T7 provides the essential helicase
and primase activities for the replication of the T7 genome. In addit
ion, it also displays a DNA-dependent deoxyribonucleoside triphosphata
se activity, the preferred substrate of which is dTTP. Previous invest
igations have demonstrated that the translocation of the gene 4 protei
n along single-stranded DNA is blocked by the presence of benzo[alpha]
pyrene-DNA adducts and that the gene 4 protein is likely to be sequest
ered at the sites of these adducts. In the present study, we directly
show that the helicase activity of the gene 4 protein is also profound
ly inhibited by the benzo[alpha]pyrene-DNA adducts. The inhibitory eff
ects of these adducts are strand-specific in that they block the DNA h
elicase activity of the gene 4 protein only when they are located in t
he DNA strand where the gene 4 protein translocates when it unwinds do
uble-stranded DNA. Consistent with the hypothesis that the gene 4 prot
ein is sequestered at the adduct site, we also show that the complexes
formed by the gene 4 protein and benzo[alpha]pyrene-modified DNA are
far more stable than those formed by the gene 4 protein and unmodified
DNA.