Enzymes acting at strand interruptions in DNA

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Abstract
Endogenous and environmental DNA-damaging agents often generate single-strand interruptions in DNA. The lesions trigger a complex set of cellular reactions. In most eukaryotic cells, cellular poly(ADPribose) formation is the most acute response to such damage. Recently, such events have been amenable to study with soluble cell-free extracts of human cells. These investigations clarify the modulating role on DNA repair by poly (ADP-ribose), and suggest that the primary function of this unusual polymer is to act as an antirecombinant agent. Similar biochemical studies of subsequent repair events have revealed a branched pathway for the ubiquitous DNA base excision-repair process. The alternative pathway provides the cell with back-up functions for individual steps in this essential form of DNA repair.