Characterization of DNA polymerase I*, a form of DNA polymerase I found in Escherichia coli expressing SOS functions

J Biol Chem. 1985 Mar 10;260(5):3178-84.


DNA polymerase I* is a form of the DNA polymerase I isolated from Escherichia coli which are expressing recA/lexA (SOS) functions. Induction of recA or polA1 cells by nalidixic acid does not result in the appearance of pol I*, but lexA or recA mutants that are constitutive for SOS functions constitutively express pol I* and mutants which lack functional recA protein produce pol I* when they carry a lexA mutation which renders the lexA repressor inoperative. Pol I* has been induced by nalidixic acid in dinA, dinD, dinF, and umuC mutants. Polymerase I* has a lower affinity for single-stranded DNA-agarose than polymerase I and it sediments through sucrose gradients in a dispersed manner between 6.6-10.5 S, whereas polymerase I sediments at 5 S. Whereas pol I* migrates significantly faster than pol I in nondenaturing polyacrylamide gels, the active polypeptide of both forms migrates at the same rate in denaturing polyacrylamide gels. Compared with polymerase I, polymerase I* has an enhanced capacity to incorporate the adenine analog, 2-amino-purine, into activated salmon sperm DNA and a relatively low fidelity in replicating synthetic polydeoxyribonucleotides. Both the 3'----5' (proofreading) and 5'----3' (nick-translational) exonuclease activities of pol I* and pol I are indistinguishable. Estimates of processivity give a value of approximately 6 for both forms of the enzyme.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Centrifugation, Density Gradient
  • Chromatography, Affinity
  • DNA Polymerase I / metabolism*
  • DNA Repair*
  • DNA, Bacterial / biosynthesis
  • Electrophoresis, Polyacrylamide Gel
  • Escherichia coli / enzymology*
  • Escherichia coli / genetics
  • Mutation
  • Poly dA-dT / metabolism


  • DNA, Bacterial
  • Poly dA-dT
  • DNA Polymerase I