Arrest of DMA Elongation by DMA Polymerases at Guanine Adducts on 4-Hydroxyaminoquinoline 1-Oxide-modified DMA Template1

In vitro modification of M13 phage single-stranded DMA with 4-hydroxyaminoquinoline 1-oxide (4HAQO) resulted in four kinds of adducts: three guanine adducts, QGh QGn, and QGm;and one adenine adduci, QA, at ratios of 16.4 47.3, 13.7, and 22.6, respectively. The carcinogen-modified DMA, initiated with a se quence-defined oligodeoxynucleotide primer, was replicated in vitro with Escherichia coli DNA polymerase I (Klenow fragment) and calf thymus DNA polymerases o and ß. The reaction prod ucts were analyzed on a DNA-sequencing gel. DNA elongation by DNA polymerase I was arrested at putative guanine adducts on the template in three ways: at one base prior to guanine; at positions opposite to guanine; and at one base beyond guanine. Similar patterns of elongation arrest were also obtained with the mammalian DNA polymerases a and ß.In contrast to guanine adducts, the adenine adduci, QA, might lack the capacity to arrest DNA chain elongation by DNA polymerases.