title: Proteins tightly bound to DNA and DNA-synthesizing activity of nucleoids from Escherichia coli.
abstract: Membrane-attached nucleoids were isolated from E. coli and separated from proteins by 2 M NaCl. Disintegration of such nucleoids by ultrasound and subsequent centrifugation resulted in the formation of two fractions: a sediment (fraction I) and a supernatant (fraction II). The protein:DNA ratio of fraction I was equal to 27 and was different from that to fraction II (2.6). More than 70% of the proteins not dissociating at 2 M NaCl and bound to DNA of both fractions were polypeptides with molecular weights (Mw) of 31,000-23,000 daltons (31-23 Kdal). After pulse labelling of the cells with [3H]-thymidine, the specific radioactivity of newly synthesized DNA associated with fraction I was shown to be considerably higher than that of fraction II. The analysis of DNA-synthesizing activities in fractions I and II showed that both nucleoid fractions contained DNA polymerase I. After dissolving the two fractions in 8 M urea - 0.15% sodium dodecylsulphate (SDS) they were chromatographed on hydroxyapatite. DNA-protein complexes were obtained that did not dissociate at 4 M guanidine X HCl - 5 M urea and 1% SDS. The main protein of the complexes was a 31 Kdal polypeptide tightly bound to DNA.
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis / Q000378:metabolism*; D002876:Chromosomes, Bacterial / Q000032:analysis*; D004269:DNA, Bacterial / Q000096:biosynthesis / Q000378:metabolism*; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D003720:Densitometry; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D010455:Peptides / Q000032:analysis; D012329:RNA, Bacterial / Q000032:analysis
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D010455:Peptides; D012329:RNA, Bacterial; D004259:DNA-Directed DNA Polymerase