Repair replication of DNA in ultraviolet-irradiated HeLa-S3 cells has been examined and shown to continue for many hours after irradiation. The rate of repair replication decreases with time, but approaches zero slowly; the decline in rate with time is similar for all doses studied, from 24 to 624 ergs/mm2 at 254 nm. Cells in S-phase exhibit the same rates of repair and pattern of decline in rate as do unsynchronized cells. The size of the repair patches produced at different times after irradiation does not vary. The initial rates of repair replication are linear with dose up to about 150 ergs/mm2; above 300 ergs/mm2, no further increase in initial rate is evident. The dose - response data suggest that repair replication may be rate limited by an enzyme in the repair pathway.
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