Enzymatic DNA Degradation in E. coli: Its Relationship to Synthetic Processes at the Chromosome Level

Evidence that degradation processes occur along the E. coli chromosome is supplied by the discovery of repair mechanisms that remove altered stretches of DNA and replace them with newly synthesized ones (Setlow and Carrier, 1964; Boyce and Howard-Flanders, 1964a; Pettijohn and Hanawalt, 1964). In addition, there are indications that genetic recombination is a nuclease-mediated process: not only does it appear to take place by ‘breakage and rejoining’ (Siddiqi, 1963; Oppenheim and Riley, 1966), but recombination-deficient mutants release an abnormal quantity of deoxyribonucleotides when their DNA is submitted to injurious treatments (Clark et al., 1966; Howard-Flanders and Boyce, 1966). Nucleases may also play a role in DNA replication: as recently reviewed by Lehman (1967), such a role is suggested both by the association of changes in nucleolytic activity and in the rate of DNA synthesis and by the effect of DNases on the ‘primer’ properties of purified DNA.