Fapyadenine is a moderately efficient chain terminator for prokaryotic DNApolymerases

Hypoxanthine\xanthine oxidase\Fe3+\ethylenediaminetetraacetate (EDTA) was u sed to modify ss M13 mp18 phage DNA. The dominant base modifications found by GC/IDMS-SIM were FapyGua, FapyAde, 8-hydroxyguanine, and thymine glycol. Analysis of in vitro DNA synthesis on oxidatively modified template by thr ee DNA polymerases revealed that T7 DNA polymerase and Klenow fragment of p olymerase I from Escherichia coli were blocked mainly by oxidized pyrimidin es in the template whereas some purines that were easily bypassed by the pr okaryotic polymerases constituted a block for DNA polymerase beta from calf thymus. DNA synthesis by T7 polymerase on poly(dA) template, where FapyAde content increased 16-fold on oxidation, yielded a final product with a dis crete ladder of premature termination bands. When DNA synthesis was perform ed on template from which FapyAde, FapyGua, and 8OHGua were excised by the Fpg protein new chain terminations at adenine and guanine sites appeared or existing ones were enhanced. This suggests that FapyAde, when present in D NA, is a moderately toxic lesion. Its ability to arrest DNA synthesis depen ds on the sequence context and DNA polymerase. FapyGua might possess simila r properties. (C) 2000 Elsevier Science Inc.