Proteins Involved in Chromosome Partitioning and DNA Organization

Several proteins are known to be involved chromosome organization and partitioning. Soj (ParA) and Spo0J (ParB) of B. subtilis belong to a family of conserved proteins required for efficient plasmid and chromosome partitioning in many bacterial species. We found that soj null mutations cause a defect in chromosome partitioning when combined with a null mutation in smc. smc encodes the structural maintenance of chromosome protein that is highly conserved and involved in chromosome compaction and partitioning. We also found that soj null mutations caused increased initiation of DNA replication and were partly defective in separation of sister copies of the region around the origin of replication. Null mutations in spo0J are also synthetic with smc and cause defects in separation of sister origin regions. soj and spo0J also contribute to regulation of replication initiation, although the mechanism is not yet known.