Analysis of the Locus Involved in Plasmid Partitioning for the Native Agrobacterium Plasmid pTAR

Abstract

Stable inheritance of DNA is a problem which every cellular system must resolve. In eukaryotes, the inheritance of the chromosomal DNA is ensured by way of centromeric interaction with cellular mitotic spindle fibers. Because prokaryotes lack such fibers, they must resolve the same problem in a different way. This partitioning process is not well understood for such cells. It has been suggested that prokaryotic DNA interacting with the cell membrane in the form of mesosomes (1) acts as the prokaryotic analog of the eukaryotic spindle fiber-centromere complex in accomplishing DNA partitioning. Plasmids from prokaryotic systems have proven useful as model systems in the study of DNA replication and copy number control. They have also been found to control their own partitioning (2, 3, 4, 5). It has been suggested that plasmids may interact with the cellular membrane as does chromosomal DNA (6) or closely associate themselves with the chromosome at least during cellular division in order to achieve proper partitioning (7, 8) although the evidence to date has only been circumstantial. It is becoming clear that among the different plasmids so far studied, there are at least two approaches to the problem of stable inheritance. One approach relies on random or passive distribution to the daughter cells for plasmids which are maintained in high copy number (9).