Inhibition of DNA replication by ionizing radiation is mediated by a trans-acting factor.

Gamma irradiation of a human cell line containing an extrachromosomal plasmid results in inhibition of the replication of both genomic and plasmid DNA. This inhibition is observed at doses of radiation which produce an insignificant amount of damage in the plasmid DNA molecules. These results indicate that radiation-induced inhibition of DNA replication is mediated by a trans-acting factor.