Haloferax volcanii

The model shown in Fig. 17 is based on the integration of morphological data obtained with S-layers from Haloferax volcanii [121] and of chemical data obtained with S-layers from Halobacterium halobium [117]. The integration of experimental data from different organisms in one and the same model is unsatisfactory. However, a recent study of the chemical structure of the glycoprotein of Haloferax volcanii by Sumper et al. [122] has shown that the most important domains for model building found in Halobacterium halobium are also present in the glycoprotein of Haloferax volcanii ... 

The three-dimensional reconstruction from a tilt series of a negatively stained cell envelope revealed a dome-shaped morphological imit with a wide opening toward the cytoplasmic membrane and a narrow opening to the exterior at the apex [125]. This design resembles that of Haloferax volcanii [121] and, to a lesser extent, that of Sulfolobus... 

Haloferax (formerly Halobacterium) volcanii, a moderately halophilic species. A close relative of Haloferax volcanii is Haloferax phenon K isolate Aa 2.2 [4]. Halobacterium marismortui, the subject of extensive work on ribosomal proteins, is not closely related to Halobacterium salinarium, instead, it belongs in the genus Haloarcula [2]. 

Using an in situ lysis method, Gutierrez et al. [20] electrophoretically surveyed sixty-five halobacterial strains for the presence of large plasmids. Three quarters of the strains had plasmids visible by this method, the majority containing three or four [20]. Due to the limitations of the electrophoretic technique used, this analysis no doubt missed some of the largest plasmids (such as the largest Haloferax volcanii plasmid [15]). 

An indication of the diversity of plasmids that might be found in wild populations of halobacteria is given by the characterization of three new isolates of Haloferax volcanii, each of which contains a different plasmid (3, 5, and 44 kbp). These plasmids do not hybridize with each other or with the 6.4 kbp plasmid pHV2 from the original Haloferax volcanii isolate DS2. One of the plasmids was shown to be compatible with pHV2[28]. 

Haloferax volcanii is particularly attractive as a halobacterial experimental system because it is a relatively fast grower and is capable of growing on a simple minimal medium [53], so that there is the possibility of isolating auxotrophic strains and thus identifying genes for many biosynthetic functions. Auxotrophic strains and methods for mating [53] and protoplast fusion [28] of Haloferax volcanii have been developed. 

For these reasons, Haloferax volcanii seemed to be a good subject for a genome mapping project. Physical mapping of the genomes of two other halobacteria is now also underway Halobacterium sp. GRB [Charlebois, R.L., personal communication], Halobacterium halobium NRCl [Hackett, N., personal communication]. 

Transformation with cosmid DNA from the Haloferax volcanii minimal set has been used to map 140 ethylmethanesulfonate-induced mutants requiring one of 14 amino acids, uracil, adenine, or guanine. This has added an additional 35 loci to the map, most represented by several mutants in the collection. Some indicate operons, such as the 19 arg mutations mapped to the overlap between cosmids 21 and 247, as well as the neighboring part of cosmid 21. Other loci are likely to contain single genes, such as some of the four unlinked his loci [86]. 

Fig. 2. Map of the Haloferax volcanii genome (top) the chromosome (bottom) the plasmids. Cosmids are represented by arrows, site-rich regions (oases) by heavy line, and markers placed by hybridization with unique probes are shown inside the circle (all from ref. [15]). Outside the circle are the results of probing with repeated sequences (ISH51, D), with labelled tRNA, 7S and ribosomal RNAs and (outermost) auxotrophic markers mapped by complementation. From ref. [86].

RNase P, which removes the 5 leader from tRNA transcripts, contains an RNA moiety in bacteria, eucarya, and archaea. The enzyme from Haloferax volcanii has been purified and the 345-nucleotide RNA portion used to generate a probe for cloning of the corresponding gene [123]. The sequence can be folded into a structure similar to that of bacterial RNase P RNAs. SI nuclease and primer extension localize the 5 end of the transcript adjacent to four potential archaeal promotor sequences. An in vitro transcript corresponding to the native RNA plus twenty 5 and nine 3 flanking nucleotides did not by itself exhibit RNase P activity (as bacterial RNase P RNAs do), under a variety of conditions. It was, however, able to reconstitute an active enzyme in combination with the protein moiety from Bacillus subtilis. This indicates that in Haloferax volcanii the RNase P RNA is the catalytic part of the enzyme but it may require some structural help [123]. 

Haloferax volcanii mutants resistant to the competitive dihydrofolate-reductase inhibitor trimethoprim contain amplifications of various lengths of DNA from a particular region and overproduce a particular protein [166], which proved to be dihydrofolate reductase. The dhf gene was cloned from one of the amplification mutants, and its sequence can... 

A homologue of the E. coli hisC gene was isolated by transformation of the his, arg" Haloferax volcanii strain WR256 with cosmid DNAs from the Haloferax volcanii minimal set. The deduced amino-acid sequence can be aligned with corresponding bacterial and eucaryal enzymes, with which it is identical at approximately 20 (yeast) or 30 E. coli or Bacillus subtilis) percent of positions. E. coli and B. subtilis are in turn only 30% identical [65]. The strain had previously been shown to be transformable... 

Rpnnekleiv M. and Liaaen-Jensen S. (1995) Bacterial carotenoids 53, Cso-carotenoids 23, Carotenoids of Haloferax volcanii versus other halophilic bacteria. Biochem. Sys. Ecol. 23, 627-634. 

Haloferax volcanii Escherichia coli Homo sapiens... 

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