title: A protein covalently bound to ColE1 DNA.
abstract: ColE1 DNA was isolated from Escherichia coli as a relaxation complex of supercoiled DNA and proteins. Treatment of the complex with either protein-denaturing agents (SDS, phenol etc.) or proteolytic enzymes converted the supercoiled DNA to an open-circular form (relaxation). The relaxation complex was separately labelled in vivo with [3H]Leu or [14C]Leu, [35S]Met or (32P)phosphate and extensively purified. Complete hydrolysis of the relaxed complex with DNase I and P1 nuclease produced a 36-kDa protein which, we believe, is covalently bound to ColE1 DNA. On the other hand, the relaxed complex was treated with tosylphenylalanylchloromethane-treated-trypsin and the DNA-peptide(s) produced was (were) isolated and digested with the nucleases as above. The resulting nucleotidylpeptide(s) was (were) isolated by DEAE-Sephadex chromatography. The only 5'-dCMP was released from the nucleotidylpeptide(s) by snake venom phosphodiesterase treatment. O-Phosphoserine was found in acid hydrolysates of the DNA-peptide(s). We suggest that in the relaxation event the 36-kDa protein becomes covalently linked to ColE1 DNA via a phosphodiester bond between dC and the serine residue.
mesh_terms: D002499:Centrifugation, Density Gradient; D004269:DNA, Bacterial / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D007930:Leucine / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D009690:Nucleic Acid Conformation; D010710:Phosphates / Q000378:metabolism; D010957:Plasmids; D011506:Proteins / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D010710:Phosphates; D011506:Proteins; D008715:Methionine; D003850:Deoxyribonuclease I; D007930:Leucine