The ftsZ gene of Haloferax mediterranei: sequence, conserved gene order, and visualization of the FtsZ ring

We sequenced the ftsZ gene region of the halophilic archaeon Haloferax medi terranei and mapped the transcription start sites for the ftsZ gene. The ge ne encoded a 363-amino-acid long FtsZ protein with a predicted molecular ma ss of 38 kDa and an isoelectric point of 4.2. A high level of similarity to the FtsZ protein of Haloferax volcanii was apparent, with 97 and 90% ident ity at the amino acid and nucleotide levels, respectively. Structural conse rvation at the protein level was shown by visualization of the FtsZ ring st ructure in H. mediterranei cells using an antiserum raised against FtsZ of H. volcanii FtsZ rings were observed in cells in different stages of divisi on, including cells with pleomorphic shapes and cells that appeared to be u ndergoing asymmetric division. Cells were also observed that displayed cons triction-like invaginations in the absence of an FtsZ ring, indicating that morphological data are not sufficient to determine whether pleomorphic Hal oferax cells are undergoing cell division. Both the upstream and downstream gene order in the ftsZ region was found to be conserved within the genus H aloferax. Furthermore, the downstream gene order, which includes the secE a nd nusG genes, is conserved in almost all euryarchaea sequenced to date. Th e secE and nusG genes are likely to be transcriptionally and translationall y coupled in Haloferax, and this co-expression may have been a selective fo rce that has contributed to keeping the gene cluster intact. (C) 2000 Elsev ier Science B.V. All rights reserved.