Utilization of subsidiary chromosomal replication terminators in Bacillus subtilis

The Bacillus subtilis merodiploid strain GSY1127 contains a large nontandem duplication of a portion of its chromosome within its left (anticlockwise) replication segment. This causes displacement of the replication terminus region to a noticeably asymmetric location relative to oriC. The utilizatio n of the subsidiary replication terminators, TerIII and TerV in the merodip loid strain has been compared with that in B. subtilis 168. It is shown tha t TerIII is utilized to a significant extent in GSY1127 and that TerV is us ed only marginally at the most. Neither of these terminators is used to a m easurable extent in the 168 strain. It is concluded that TerIII and TerV do indeed function as backups to the major terminator TerI, as has been gener ally thought. It is further concluded that, in the 168 strain, the vast maj ority of clockwise forks are arrested at the highly efficient TerI terminat or, with fork fusion between the approaching forks occurring frequently whi le the clockwise fork is stationary at TerI.