IDENTIFICATION AND CHARACTERIZATION OF A NOVEL TYPE OF REPLICATION TERMINATOR WITH BIDIRECTIONAL ACTIVITY ON THE BACILLUS-SUBTILIS THETA-PLASMID PLS20

We have sequenced and analysed a 3.1 kb fragment of the 55 kb endogeno us Bacillus subtilis plasmid pLS20 containing its replication function s, Just outside the region required for autonomous replication, a segm ent of 18 bp was identified as being almost identical to part of the m ajor B. subtilis chromosomal replication terminator. Here, we demonstr ate that this segment is part of a functional replication terminator, This newly identified element, designated TerLS20, is the first replic ation terminator identified on a theta plasmid from a Gram-positive ba cterium. TerLS20 is distinct from other known replication terminators in the sense that it is functional in both orientations. The region re quired for bipolar functionality of TerLS20 was delineated to a sequen ce of 29 bp, which is characterized by an imperfect dyad symmetry.