AN ARCHAEBACTERIAL HOMOLOG OF THE ESSENTIAL EUBACTERIAL CELL-DIVISIONPROTEIN FTSZ

Life falls into three fundamental domains-Archaea, Bacteria, and Eucar ya (formerly archaebacteria, eubacteria, and eukaryotes, respectively) , Though Archaea lack nuclei and share many morphological features wit h Bacteria, molecular analyses, principally of the transcription and t ranslation machineries, have suggested that Archaea are more related t o Eucarya than to Bacteria, Currently, little is known about the archa eal cell division apparatus, In Bacteria, a crucial component of the c ell division machinery is FtsZ, a GTPase that localizes to a ring at t he site of septation, Interestingly, FtsZ is distantly related in sequ ence to eukaryotic tubulins, which also interact with GTP and are comp onents of the eukaryotic cell cytoskeleton. By screening for the abili ty to bind radiolabeled nucleotides, we have identified a protein of t he hyperthermophilic archaeon Pyrococcus woesei that interacts tightly and specifically with GTP. Furthermore, through screening an expressi on library of P. woesei genomic DNA, we have cloned the gene encoding this protein. Sequence comparisons reveal that the P. woesei GTP-bindi ng protein is strikingly related in sequence to eubacterial FtsZ and i s marginally more similar to eukaryotic tubulins than are bacterial Ft sZ proteins. Phylogenetic analyses reinforce the nation that there is an evolutionary linkage between FtsZ and tubulins. These findings sugg est that the archaeal cell division apparatus may be fundamentally sim ilar to that of Bacteria and lead us to consider the evolutionary rela tionships between Archaea, Bacteria, and Eucarya.