The relative contribution of adduct blockage and DNA repair on template utilization during replication of 1,N2-propanodeoxyguanosine and pyrimido.
The role of replication blockage by the exocyclic DNA adducts propanodeoxyguanosine (PdG) and pyrimido[1,2-alpha]purin-10(3H)-one (M1G) was determined through the use of site-specifically adducted M13MB102 genomes containing a C:C-mismatch approximately 3000 base-pairs from the site of adduct incorporation. Genomes containing either dG, PdG, or M1G positioned at site 6256 of the (-)-strand were transformed into repair-proficient and repair-deficient Escherichia coli strains and the percent template utilization was determined by hybridization analysis. Unmodified genomes containing a C:C-mismatch resulted in a percent template utilization of approximately 60 and 40% for the (-)- and (+)-strands, respectively. Transformation of PdG- or M(1)G-adducted genomes resulted in approximately a 60-40% and 50-50% (-)-strand to (+)-strand ratio, respectively, indicating that PdG and M(1)G are negligible blocks to replication in repair-proficient E. coli. This is in contrast to previous studies using (PdG:T)- and (M1G:T)-mismatched M13MB102 genomes, which resulted in a majority of the replication events using the unadducted (+)-strand and suggested that both adducts were significant blocks to replication [J. Biol. Chem. 272 (1997) 11434; Proc. Natl. Acad. Sci. U.S.A. 94 (1997) 8652]. The C:C-mismatch results, though, indicate that the large strand bias detected in the earlier studies is due to repair of the adducts and resynthesis of the (-)-strand using the (+)-strand as a template for repair synthesis. Transformation of adducted C:C-mismatched genomes into E. coli strains deficient in nucleotide excision repair did result in an increased strand bias with only approximately 20 and 34% of the replication events using the (-)-strand for PdG- and M1G-adducted genomes, respectively. The increased strand bias indicates the importance of nucleotide excision repair in the removal of PdG and M1G.
A.B. Hancock, Jr., Memorial Laboratory for Cancer Research, The Vanderbilt-Ingram Cancer Center, Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232-0146, USA.
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D017104:Bacteriophage M13 / Q000235:genetics*; D020137:Base Pair Mismatch; D018736:DNA Adducts / Q000378:metabolism*; D004260:DNA Repair; D004261:DNA Replication; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000378:metabolism*; D016679:Genome, Viral; D016296:Mutagenesis; D011687:Purines / Q000378:metabolism*; D011743:Pyrimidines / Q000378:metabolism*
D018736:DNA Adducts; D011687:Purines; D011743:Pyrimidines; C107643:pyrimido(1,2-a)purin-10(3H)-one; C060934:1,N(2)-propanodeoxyguanosine; D003849:Deoxyguanosine