Growth during Replication Is Bidirectional

Initiation of a second round of replication leads to a replication eye at the initiation site of replication (fig. 26.3). As synthesis proceeds the size of the replication eye becomes larger at this stage the replicating chromosome is referred to as a theta structure because it has the appearance of the Greek letter d. Semiconservative replication is consistent with the density of the autoradiographic tracks made by different parts of the chromosome after one and two rounds of replication in [3H]thymidine (see fig. 26.3). 

Evidence for bidirectional replication is supported by additional experiments. Growing bacteria were briefly ex- 

Simulated autoradiographs of the E. coli chromosome after one or more replications in the presence of [3H]thymidine. After one round of replication, the autoradiograph shows a circular structure that is uniformly labeled. The second round of replication begins with the formation of a replication eye. One branch in the replication eye is twice as strongly labeled as the remainder of the chromosome, indicating that this branch contains two labeled strands. This structure is consistent with semiconservative replication for the E. coli chromosome. 

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Growth during Replication Is Bidirectional Growth at the Replication Forks Is Discontinuous Proteins Involved in DNA Replication Characterization of DNA Polymerase I in Vitro Crystallography Combined with Genetics to Produce a Detailed Picture of DNA Poll Function... 

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