Enzymic synthesis of deoxyribonucleic acid: XVII. Some unusual physical properties of the product primed by native DNA templates

Extensive replication of a helical DNA produces a complex of primer and product which can be dissociated by denaturing treatments. The physical characteristics of the enzymic product resemble those of a native DNA except in two ways: (1) an unusual capacity to resume a helical conformation after denaturing treatments (“non-denaturability”); and (2) appearance of a branched structure in the electron microscope. Exposure of the enzymic product to extensive protease, mild nuclease or prolonged heating treatment fails to alter its “non-denaturability”. These and other studies suggest that in the replication of native DNA the new strands are not covalently linked to the primer and that a “multiple hairpin” or “pleated” structure may develop which recovers considerable helicity following denaturing treatments. By contrast, these and other studies (described by Richardson, Inman & Kornberg, 1964a) also indicate that in the repair of partially single-stranded DNA, the new strands are covalently linked to the primer and appear to have all the physical properties of naturally occurring DNA.