CHARACTERIZATION OF THE EFFECTORS REQUIRED FOR STABLE INHERITANCE OF STREPTOCOCCUS-PYOGENES PSM19035-DERIVED PLASMIDS IN BACILLUS-SUBTILIS

The low-copy-number and broad-host-range pSM19035-derived plasmid pBT2 33 is stably inherited in Bacillus subtilis cells. Two distinct region s, segA and segB, enhance the segregational stability of the plasmid. Both regions function in a replicon-independent manner. The maximizati on of random plasmid segregation is accomplished by the recombination proficiency of the host or the presence of the pBT233 segA region. The segA region contains two open reading frames (orf) [alpha and beta]. Inactivation or deletion of orf beta results in SegA(-) plasmids. Bett er than random segregation requires an active segB region. The segB re gion contains two orfs (orf epsilon and orf xi) Inactivation of either of the orfs does not lead to an increase in cell death, but orfi xi p lasmids are randomly segregated. These results suggest that pBT233 sta bilization relies on a complex system involving resolution of plasmid oligomers (segA) and on the function(s) encoded by the segB region.