title: Characterization of DNA polymerase I*, a form of DNA polymerase I found in Escherichia coli expressing SOS functions.
abstract: 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.
mesh_terms: D002499:Centrifugation, Density Gradient; D002846:Chromatography, Affinity; D004256:DNA Polymerase I / Q000378:metabolism*; D004260:DNA Repair; D004269:DNA, Bacterial / Q000096:biosynthesis; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D009154:Mutation; D011067:Poly dA-dT / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D011067:Poly dA-dT; D004256:DNA Polymerase I