Repair of Single-Strand Deoxyribonucleic Acid Breaks in Ultraviolet Light-IrradiatedHaemophilus influenzae

Abstract

The wild-type strain and mutants of Haemophilus influenzae, sensitive or resistant to ultraviolet light (UV) as defined by colony-forming ability, were examined for their ability to perform the incision and rejoining steps of the deoxyribonucleic acid (DNA) dark repair process. Although UV-induced pyrimidine dimers are excised by the wild-type Rd and a resistant mutant BC200, the expected single-strand DNA breaks could not be detected on alkaline sucrose gradients. Repair of the gap resulting from excision must be rapid when experimental conditions described by us are employed. Single-strand DNA breaks were not detected in a UV-irradiated sensitive mutant (BC 100) incapable of excising pyrimidine dimers, indicating that this mutant may be defective in a dimer-recognizing endonuclease. No single-strand DNA breaks were detected in a lysogen BC100(HPlcl) irradiated with a UV dose large enough to induce phage development in 80% of the cells.

Thymineless Death in Bacillus subtilis : Correlation Between Cell Lysis and Deoxyribonucleic Acid Breakdown

“…There is evidence that repair of DNA breaks by DNA polymerase I takes place in the absence of thymine (3,31,39). A correlation between poor repair of lesions in ultraviolet light-irradiated DNA and cell lysis was suggested by Kantor and Barnhart (18).…”

Thymineless Death in Bacillus subtilis : Correlation Between Cell Lysis and Deoxyribonucleic Acid Breakdown

“…There is evidence that repair of DNA breaks by DNA polymerase I takes place in the absence of thymine (3,31,39). A correlation between poor repair of lesions in ultraviolet light-irradiated DNA and cell lysis was suggested by Kantor and Barnhart (18). There is conflicting evidence concerning the extent of DNA breakdown during thymine starvation (1, 35, 40).…”