+1 Recommend
0 collections
      • Record: found
      • Abstract: found
      • Article: not found

      Formation of a DNA loop at the replication fork generated by bacteriophage T7 replication proteins.

      The Journal of Biological Chemistry

      DNA, Single-Stranded, genetics, Bacteriophage T7, Base Sequence, Biotinylation, DNA, DNA Helicases, metabolism, ultrastructure, DNA Primase, DNA Primers, DNA Replication, DNA, Circular, Bacteriophage M13, DNA, Viral, DNA-Binding Proteins, DNA-Directed DNA Polymerase, Deoxycytosine Nucleotides, chemistry, Molecular Sequence Data, Protein Binding, Viral Proteins

      Read this article at

          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.


          Intermediates in the replication of circular and linear M13 double-stranded DNA by bacteriophage T7 proteins have been examined by electron microscopy. Synthesis generated double-stranded DNA molecules containing a single replication fork with a linear duplex tail. A complex presumably consisting of T7 DNA polymerase and gene 4 helicase/primase molecules was present at the fork together with a variable amount of single-stranded DNA sequestered by gene 2.5 single-stranded DNA binding protein. Analysis of the length distribution of Okazaki fragments formed at different helicase/primase concentrations was consistent with coupling of leading and lagging strand replication. Fifteen to forty percent of the templates engaged in replication have a DNA loop at the replication fork. The loops are fully double-stranded with an average length of approximately 1 kilobase. Labeling with biotinylated dCTP showed that the loops consist of newly synthesized DNA, and synchronization experiments using a linear template with a G-less cassette demonstrated that the loops are formed by active displacement of the lagging strand. A long standing feature of models for coupled leading/lagging strand replication has been the presence of a DNA loop at the replication fork. This study provides the first direct demonstration of such loops.

          Related collections

          Author and article information



          Comment on this article