The bacterial ParA-ParB partitioning proteins

A pair of genes designated parA and parB are encoded by many low copy numbe r plasmids and bacterial chromosomes. They work with one or more cis-acting sites termed centromere-like sequences to ensure better than random prediv isional partitioning of the DNA molecule that encodes them. The centromere- like sequences nucleate binding of ParB and titrate sufficient protein to c reate foci, which are easily visible by immuno-fluorescence microscopy. The se foci normally follow the plasmid or the chromosomal replication oriC com plexes. ParA is a membrane-associated ATPase that is essential for this sym metric movement of the ParB foci. In Bacillus subtilis ParA oscillates from end to end of the cell as does MinD of E. coli, a relative of the ParA fam ily. ParA may facilitate ParB movement along the inner surface of the cytop lasmic membrane to encounter and become tethered to the next replication zo ne. The ATP-bound form of ParA appears to adopt the conformation needed to drive partition. Hydrolysis to create ParA-ADP or free ParA appears to favo ur a form that is not located at the pole and binds to DNA rather than the partition complex. Definition of the protein domains needed for interaction with membranes and the conformational changes that occur on interaction wi th ATP/ADP will provide insights into the partitioning mechanism and possib le targets for inhibitors of partitioning. (C) 2001 Elsevier Science B.V. A ll rights reserved.