ParC, a New Partitioning Protein, Is Necessary for the Active Form of ParA From pMF1 Plasmid.

The ParABS partitioning system, a main driver of DNA segregation in bacteria, employs two proteins, ParA and ParB, for plasmid partition. The pMF1 plasmid from 124B02 has a operon encoding a small acidic protein, ParC, in addition to type I ParA and ParB homologs. Here, we show that expression of upstream of (as in the natural case), but not ectopic expression, is essential for the plasmid inheritance in cells. Co-expression of upstream of was determined to form a soluble ParC-ParA heterodimer at a 1:1 ratio, while individual expression of or co-expression of with ectopic formed insoluble ParA proteins. Purified ParA proteins alone had no ATPase activity and was easily dimerized, while mixing ParA with ParC formed the ParC-ParA heterodimer with the ATPase and polymerization activities. Fusing ParC and ParA also produced soluble proteins and some chimeras restored the ATPase activity and plasmid inheritance. The results highlight that proximal location of before is critical to realize the functions of ParA in the partition of plasmid pMF1 and shed light on a new mechanism to realize a protein function by two separate proteins.