The partition region of plasmid QpH1 is a member of a family of two trans-acting factors as implied by sequence analysis.

Sequencing analysis revealed that the partition region of the Coxiella burnetii plasmid QpH1 contains a putative operon, designated qsopAB. The two open reading frames (ORFs), qsopA and qsopB, specify the QsopA and QsopB proteins, with deduced molecular masses of 45.7 and 37.6 kDa, respectively. Maxicell analysis demonstrated that although qsopB was located downstream from qsopA, it had its own promoter that was active in Escherichia coli. Several direct or inverted repeats were found around this operon. The most distinct was a 20-bp long imperfect palindrome in the promoter region of qsopA, with homology to a palindrome in the promoter region of P1 parA. Structurally qsopAB was similar to parAB of the P1 plasmid. However, at the amino acid (aa) sequence level, QsopA and QsopB were closest to the F plasmid SopA and SopB proteins, respectively. QsopA shared 58.0% homology and 32.7% identity with SopA, but only 45-50% homology and 22-26% identity with other members of the protein A partition family. QsoB had even lower (41-45%) homology to other members of the protein B partition family, with the highest homology and identity to SopB. Despite lower homologies, both QsopA and QsopB did share conserved aa sequence regions and invariant residues with other members within each family.