|Bacteria Escherichia coli
|Breier AM, Weier HU, Cozzarelli NR. Independence of replisomes in Escherichia coli chromosomal replication. Proc Natl Acad Sci U S A. 2005 Mar 15 102(11):3942-7 p.3945 right column top paragraphPubMed ID15738384
|P.3944 left column 3rd paragraph: "Single-Molecule Analysis of Replication with DNA Combing: [Investigators] first sought to discriminate among the independent, semiindependent, and coupled replisome factory models (Fig. 1E) by using DNA combing (ref 26). Combing allows the visualization of the replicated regions of long molecules of genomic DNA that have been bound and stretched on glass. The major advantage of a single DNA molecule method such as combing is that, unlike ensemble methods, it discriminates between variation among cells and variation within cells. If all replications were unidirectional but in a random direction, an ensemble measurement would show equal leftward and rightward replication and lead to the erroneous conclusion that replication is bidirectional. In [their] case, measuring the relative positions of the left and right replisomes on individual chromosomes should distinguish among the three models."
|P.3945 left column bottom paragraph: "[Investigators] plotted the distance of each fork from the origin versus time (Fig. 4C ). [They] draw three conclusions from these data. First, the average rate of replication is constant for both forks. The data for each replisome fit very well to a straight line (R^2 = 0.992 and 0.972 for the left and right forks, respectively). Second, the average speeds of the two forks are, within error, identical: 604 nt/s for the left replisome and 617 nt/s for the right at 30°C. Thus, the forks move at nearly the same speed throughout elongation. These values are consistent with the speed of 1 kb/s at 37°C previously measured for DNA polymerase III (ref 1). Third, the left replisome was farther from the origin by ≈150 kb. Thus, the only consistent difference between the two replisomes occurs at or just after initiation, when the leftward replisome establishes a lead. This difference is compatible only with the independent model." Value is average of left and right replisomes. See BNID 103995