ABSTRACT
We have analyzed DNA polymerase function in repair synthesis in human diploid fibroblasts. Previous studies from many laboratories have resulted in confusing and apparently contradictory findings; our studies suggest a unifying hypothesis and indicate that previous results may not actually be in conflict. Nongrowing (confluent) cells were damaged with N-methyl-N-nitrosourea (MNU), bleomycin, X- ray, UV radiation, or N-acetoxy-2-acetylaminofluorene (NA-AAF) over a wide range of doses, and repair synthesis was studied in the presence of one of three polymerase inhibitor, aphidicolin, dideoxythymidine triphosphate (ddTTP), or N-ethyl maleimide. We find that both polymerase a and a non-a polymerase, probably polymerase β, are involved in repair synthesis. Furthermore, there is a dose dependence for polymerase function: at low doses of damage repair synthesis is mediated primarily by the non-α polymerase; as the amount of damage is increased, polymerase α participates to an increasing extent and at high levels of damage is responsible for ~50-80% of the repair synthesis. In a study in rapidly growing cells, repair synthesis following a high dose of UV was refractory to aphidicolin; these findings indicate that in growing and quiescent cells DNA polymerases may function differently in repair synthesis. All of the above results may be analyzed in terms of a simple model in which two repair synthesis systems, each involving one of the polymerases, compete to put repair patches into damaged DNA.
