Cellular location of origin and terminus of replication in Bacillus subtilis.

The origin of replication of Bacillus subtilis 168 trp thy dna-1 (temperature-sensitive initiation mutant) was labeled with [3H]thymidine. Analysis of labeled cells by autoradiography revealed that most of the radioactivity was associated with cell pole areas. To label the terminus, cells that had initiated were treated with chloramphenicol to inhibit cell growth and division but to allow continued DNA synthesis. These cells were then labeled with [3H]thymidine at a time when chromosome replication was nearly complete. The distribution of radioactivity was similar to that observed in origin-labeled cells. In contrast, exponentially growing cells that were labeled for a brief time at the permissive temperature showed a random distribution of radioactivity. These data indicate that the origin and terminus of replication are located at cell poles.