Evidence for the lack of deoxyribonucleic acid dark-repair in Halobacterium cutirubrum.

1. Halobacterium cutirubrum does not perform dark-repair of DNA either after u.v. irradiation or during normal growth. 2. Cultures irradiated with u.v. are readily photoreactivated, but do not recover viability in the dark. 3. No increase in the rate of DNA synthesis is observed in the surviving cells after u.v. irradiation. 4. At early times during normal semiconservative replication, newly incorporated thymidine is found only in the hybrid DNA. 5. It is suggested that these bacteria may be useful in the study of DNA replication and photoreactivation.