Ultraviolet radiation inhibits replicon initiation in S phase human cells.

DNA replication was examined in ultraviolet-irradiated human fibroblasts and HeLa cells. The principal effect of exposures to low radiation fluences (less than 1.3 J/m2) was a reduced synthesis of molecules about one-half replicon in size resulting from an inhibition of replicon initiation. As the fluence of radiation was increased, inhibitory effects on strand elongation and joining masked the effect on replicon initiations.