Excision of thymine dimers from specifically incised ultraviolet irradiated DNA by E. coli DNA polymerase I is stimulated by concurrent DNA synthesis. The 36,000 molecular-weight "small fragment" obtained by limited proteolysis of DNA polymerase I, which retains only the 5′ → 3′ exonuclease activity, also excises thymine dimers, but at one-tenth the rate of the intact enzyme. However, the rate of excision is increased by addition of the "large" 76,000-molecular weight fragment. With the further addition of the 4 deoxynucleoside triphosphates, permitting DNA synthesis to occur, excision approaches rates observed with the intact enzyme. The same result was obtained with a fragment of DNA polymerase I with 5′ → 3′ exonuclease activity that is present uniquely in polymerase I amber mutants. © 1974.
Friedberg, E. C., & Lehman, I. R. (1974). Excision of thymine dimers by proteolytic and amber fragments of E. coli DNA polymerase I. Biochemical and Biophysical Research Communications, 58(1), 132–139. https://doi.org/10.1016/0006-291X(74)90901-2