Cell sorting protein homologs reveal an unusual diversity in archaeal cell division

In this issue of PNAS, Lindås et al. (1) report an interesting diversity in archaeal cell division, in contrast to those of bacterial and eukaryotic cells, which appear to be more uniform. The Archaea, Bacteria, and Eucarya constitute the 3 domains of life on our planet (2). Within the cell cycle of each lineage, DNA replication ensures faithful duplication of the chromosome, after which a copy of the genetic material from the mother cell segregates into 2 daughter cells. By this process, organisms generate progeny to ensure continuation of their lineage. In their seminal report, Woese et al. (2) subdivided Archaea into 2 major kingdoms, namely the Euryarchaeota and Crenarchaeota, although as discussed later, there appear to be more kingdoms within the Archaea.

Years of comprehensive studies have provided very good insights into cell division in bacteria and eukaryotes, and although the first genome sequence of an archaeon suggested that archaea share similar replication machinery with eukaryotes, it appeared that the archaeal cell division proteins were of the bacterial type (3). Thus, the Methanocaldococcus jannaschii genome encoded 2 FtsZ, 1 FtsJ, and 3 MinD proteins. In bacteria and eukaryotic organelles, such as chloroplasts, which are known to have bacterial origin, FtsZ serves as the hallmark of cell division. This protein is a structural homolog of tubulin (4) and is required for the septation that leads to cell division and 2 daughter cells. FtsZ functions by assembling into a ring that marks the future site of cell division (5), and the Min system, including MinD, functions as an inhibitor that allows assembly only at the right place and the right time (5, 6). In agreement with the report on M. jannaschii, an examination of the publicly available databases shows that the euryarchaeal genomes have at least a homolog of …

¹E-mail: icann{at}illinois.edu