title: A DNA-unwinding protein isolated from Escherichia coli: its interaction with DNA and with DNA polymerases.
abstract: A DNA-unwinding protein has been purified to homogeneity from E. coli. This protein has a molecular weight of about 22,000, as judged by its electrophoretic mobility on polyacrylamide gels containing sodium dodecylsulfate, and it appears to be present in about 800 copies per log-phase cell. It binds tightly and cooperatively to single-stranded DNA, and much less tightly, if at all, to RNA or double-stranded DNA. Like the T4 gene-32 protein characterized previously, the E. coli DNA-unwinding protein depresses the melting temperature of double-stranded DNAs, with regions rich in A-T base-pairs being preferentially melted. The E. coli protein strongly stimulates in vitro DNA synthesis by E. coli DNA polymerase II on appropriate templates; however, no stimulation is found with purified polymerases I or III of E. coli, or with T4 DNA polymerase. In contrast, gene-32 protein stimulates only the T4 DNA polymerase in a parallel assay.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002384:Catalysis; D002499:Centrifugation, Density Gradient; D003597:Cytosine Nucleotides / Q000378:metabolism; D004254:DNA Nucleotidyltransferases / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism*; D004926:Escherichia coli / Q000032:analysis; D006160:Guanosine Triphosphate / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008854:Microscopy, Electron; D009691:Nucleic Acid Denaturation; D011485:Protein Binding; D013696:Temperature; D013942:Thymine Nucleotides / Q000378:metabolism; D014316:Tritium
chemical_list: D001426:Bacterial Proteins; D003597:Cytosine Nucleotides; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004279:DNA, Viral; D013942:Thymine Nucleotides; D014316:Tritium; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D004254:DNA Nucleotidyltransferases; D008274:Magnesium