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At least 199 records · Page 11Linked to original sources
PubMed1990

Nucleotide sequence of four genes encoding ribosomal proteins from the 'S10 and spectinomycin' operon equivalent region in the archaebacterium Halobacterium marismortui.

Four genes encoding ribosomal proteins HmaS17, HmaL14, HmaL24 and HS3, have been identified in the lambda EMBL3 clone PP*7 from a genomic library of the archaebacterium Halobacterium marismortui. The clone contains genes from the 'S10 and spectinomycin' operon equivalent region. Three of the deduced proteins are homologous to the corresponding Escherichia coli and Methancoccus vannielii S17, L14 and L24 proteins, as well as to eukaryotic proteins from rat or yeast. HS3 was identified as an extra protein corresponding to the gene product for orfc in M. vannielii and the eukaryotic ribosomal protein RS4 from rat. The equivalence of HmaL24 (HL16) and E. coli L24, which share only 28% identical amino acid residues, could now be shown by localizing the HmaL24 gene at the same position in the cluster.

Amino Acid Sequence↗
PubMed1991

The proton pump bacteriorhodopsin is a photoreceptor for signal transduction in Halobacterium halobium.

Halobacterium halobium swims by rotating its polarly inserted flagellar bundle. The cells are attracted by green-to-orange light which they can use for photophosphorylation but flee damaging blue or ultraviolet light. It is generally believed that this kind of 'colour vision' is achieved by the combined action of two photoreceptor proteins, sensory rhodopsins-I and -II, that switch in the light the rotational sense of the bundle and in consequence the swimming direction of a cell. By expressing the bacteriorhodopsin gene in a photoreceptor-negative background we have now demonstrated the existence of a proton-motive force sensor (protometer) and the function of bacteriorhodopsin as an additional photoreceptor covering the high intensity range. When the bacteriorhodopsin-generated proton-motive force drops caused by a sudden decrease in light intensity, the cells respond by reversing their swimming direction. This response does not occur when the proton-motive force is saturated by respiration or fermentation.

Bacteriorhodopsins↗
PubMed1993

Thermal transitions in the purple membrane from Halobacterium halobium.

The application of a successive annealing procedure to the scanning calorimetric endotherm of the purple membrane from Halobacterium halobium in phosphate buffer, pH 7.5, leads to five thermal transitions beneath the overall endotherm. Circular dichroism and fluorescence experiments have also been carried out with the native membrane heated at the same scan rate as in calorimetric runs (1 degrees C/min) as well as with previously heated membrane samples. These results, together with others from the literature, have been used to suggest a preliminary explanation of the five thermal transitions.

Bacteriorhodopsins↗
PubMed1994

Sensitivity of Halobacterium salinarium to attractant light stimuli does not change periodically.

Halobacterium salinarium swims alternately in both directions of its cell axis. The average time between two reversals of the swimming direction is modulated by light stimuli. It is a matter of dispute whether the sensitivity to attractant stimuli depends on the time of stimulation during an interval. This question is crucial for model descriptions of the system. I have confirmed constancy of responsiveness with cells adapted to constant conditions and have reconstructed contradicting results. These are shown to be based on inadequate experimental and evaluative methods. The assumption of self-sustained oscillations which modulate sensitivity can not be justified from the attractant response.

Chemotaxis↗
PubMed1992

Alkaline p-nitrophenylphosphate phosphatase activity from Halobacterium halobium. Selective activation by manganese and effect of other divalent cations.

1. Alkaline p-nitrophenylphosphate phosphatase (pNPPase) activity of Halobacterium halobium is selectively stabilized and stimulated by Mn2+ ions. 2. Mn2+ binding to native pNPPase is characterized by a dissociation constant of 0.35 mM at pH 8.5, 37 degrees C, with a Hill coefficient of 0.988. 3. Mn2+ behaves as a mixed type nonessential activator, increasing the Vmax value (beta = 6.09, pH 8.5) and decreasing the Km value for pNPP (alpha = 0.56, pH 8.5). The Ki value for inorganic phosphate (a competitive inhibitor) was also decreased in the presence of Mn2+. 4. Activation of native pNPPase by preincubation with Mn2+ is a slow temperature-dependent process, which can be described by an exponential relationship vs time. However, a weak but immediate activation was also detected. 5. Zn2+, Cu2+ and Ni2+ were found to inhibit both native and Mn(2+)-stimulated pNPPase, whereas Co2+ and Cd2+ inhibited the Mn(2+)-stimulated pNPPase but had no effect on the native enzyme form.

4-Nitrophenylphosphatase↗
PubMed1985

Multiple promoters for the transcription of the ribosomal RNA gene cluster in Halobacterium cutirubrum.

The archaebacterium Halobacterium cutirubrum has a single ribosomal RNA transcription unit in its genomic DNA. The 5'-flanking sequence preceding the proximal 16 S gene contains two imperfect and three perfect copies of a bipartate direct repeat sequence and the first half of a long nearly perfect inverted repeat sequence that surrounds the 16 S gene. Initiation of transcription occurs within a preserved eight base segment present in each of the five direct repeat sequences. The most upstream and least conserved repeat element represents the major transcription start site and this site appears to exhibit growth rate-dependent regulation. The primary transcripts are processed near a short discontinuity within the first half of the long inverted repeat sequence to produce the 5' end of precursor 16 S rRNA.

Autoradiography↗
PubMed1987

Single crystals of large ribosomal particles from Halobacterium marismortui diffract to 6 A.

Large, well-ordered three-dimensional crystals of 50 S ribosomal subunits from Halobacterium marismortui have been obtained by seeding. The crystals have been characterized with synchrotron X-ray radiation as monoclinic, space group P2(1), with unit cell dimensions of a = 182(+/- 5) A, b = 584(+/- 10) A, c = 186(+/- 5) A, beta = 109 degrees. At 4 degrees C, the crystals (0.6 mm X 0.6 mm X 0.1 mm) diffract to 6 A resolution and are stable in the synchrotron beam for several hours. Compact packing is reflected from the crystallographic unit cell parameters and from electron micrographs of positively stained thin sections of embedded crystals.

Crystallization↗
PubMed1988

Crystallization of halophilic malate dehydrogenase from Halobacterium marismortui.

Malate dehydrogenase from the extreme halophile Halobacterium marismortui crystallizes in highly concentrated phosphate solution in space group 12 with cell dimensions a = 113.8 A, b = 122.8 A, c = 126.7 A, beta = 98.1 degrees. The halophilic enzyme was found to be unstable at lower concentrations of phosphate. It associates with unusually large amounts of water and salt, and the combined particle volume shows a tight fit in the unit cell.

Halobacterium↗
PubMed1989

Sequence, organization, transcription and evolution of RNA polymerase subunit genes from the archaebacterial extreme halophiles Halobacterium halobium and Halococcus morrhuae.

The genes for the four largest subunits, A, B', B" and C, of the DNA-dependent RNA polymerase were cloned from the extreme halophile Halobacterium halobium and sequenced and their transcription was analyzed. The downstream half of this gene cluster from another extreme halophile Halococcus morrhuae was also cloned, sequenced and its transcription products characterized. The H. halobium genes were transcribed into a common transcript from an upstream promoter in the order B", B', A and C. They are flanked by, and co-transcribed with, two smaller genes coding for 75 and 139 amino acid residues, respectively. Immediately downstream from these genes were two open reading frames that are homologous to ribosomal proteins S12 and S7 from Escherichia coli. In both extreme halophiles these genes were transcribed from their own promoter, but in Hc. morrhuae there was also considerable read-through from the RNA polymerase genes. Sequence alignment studies showed that the combined B" + B' subunits are equivalent to the B subunits of the eukaryotic polymerases I and II and to the eubacterial beta subunit, while the combined A + C subunits correspond to the A subunits of eukaryotic RNA polymerases I, II and III and to the eubacterial beta' subunit. The sequence similarity to the eukaryotic subunits was always much higher than to the eubacterial subunits. Conserved sequence regions within the individual subunits were located which are likely to constitute functionally important domains; they include sites associated with rifampicin and alpha-amanitin binding and two possible zinc binding fingers. Phylogenetic analyses based on sequence alignments confirmed that the extreme halophiles belong to the archaebacterial kingdom.

Archaea↗
PubMed1992

Solution studies of elongation factor Tu from the extreme halophile Halobacterium marismortui.

The activity, stability and structure in solution of polypeptide elongation factor hEF-Tu from Halobacterium marismortui have been investigated. The protein is stable in aqueous solutions only at high concentrations of NaCl, KCl or ammonium sulphate, whereas it is more active in exchanging GDP at lower salt concentrations. It is more active and stable at lower pH values than is non-halophilic EF-Tu. The structure in solution of the protein was determined by complementary density, ultracentrifugation, dynamic light-scattering and neutron-scattering measurements. The protein has large hydration interactions, similar to those of other halophilic proteins: 0.4 (+/- 0.1) g of water and 0.20 (+/- 0.05) g of KCl associated with 1 g of protein, with a water/KCl mass ratio always remaining close to 2. The kinetics of inactivation at low salt concentrations showed a stabilizing effect of NaCl when compared to KCl. At low salt concentration, inactivation, protein unfolding and aggregation were strongly correlated. The results suggest that the stabilization model proposed for halophilic malate dehydrogenase by Zaccai et al., involving extensive protein interactions with hydrated salt ions, is also valid for hEF-Tu.

Bacterial Proteins↗
PubMed1992

The immunity-conferring plasmid p phi HL from the Halobacterium salinarium phage phi H: nucleotide sequence and transcription.

The complete nucleotide sequence of the plasmid p phi HL, composing the central 12,041-bp L-region from the temperate phage phi H of Halobacterium salinarium is presented. Transcripts mapped to the p phi HL and the L-region produced under immune conditions, under lytic growth or constitutively, are described. The sequences upstream of the transcription start points show homology to the consensus sequence for archaeal (formerly archaebacterial) promoters. Lytic transcription is shown to be strictly time-dependent, with an early gene product required for the expression of late genes.

Bacteriophages↗
PubMed1987

The fate of thymine-containing dimers in ultraviolet-irradiated Halobacterium cutirubrum.

Extremely halophilic bacteria do not recover in the dark from the effects of ultraviolet radiation, although they can be completely photoreactivated, thus proving that pyrimidine dimers are the cytotoxic photoproducts. We have now shown, by studying the fate of thymine-containing dimers during dark liquid-holding of Halobacterium cutirubrum, that the lack of dark repair in these bacteria is due to their inability to excise such lesions, in contrast to Escherichia coli B. Nevertheless, extensive nonspecific degradation of DNA occurs in H. cutirubrum following ultraviolet irradiation, so the lack of dimer excision is not due to a generalised inability to degrade DNA after such treatment. These findings raise interesting questions concerning the basis of the resistance of halophiles to ultraviolet radiation.

DNA Repair↗
PubMed1990

Evidence for an additional archaebacterial gene cluster in Halobacterium marismortui encoding ribosomal proteins HL46e and HL30.

A small and extremely basic ribosomal protein (HL46e) has been purified from Halobacterium marismortui using reversed-phase high-performance liquid chromatography (HPLC). The amino acid sequence of the protein was determined by automated N-terminal and internal sequence analysis. Comparison of this sequence with other ribosomal protein sequences from eubacteria, archaebacteria and eukaryotes revealed a strong homology to SL46e from Sulfolobus solfataricus, YeaL46 from yeast and RL39 from rat. No significant sequence similarly was found to any eubacterial ribosomal protein so far known. Using a specific oligonucleotide probe the HL46e gene was identified, cloned and the nucleotide sequence including the 5'- and 3'-flanking regions were analysed. The HL46e gene is followed by the gene coding for HL30. A putative halobacterial promoter sequence with the motive 'TTTAAA' has been localized 32 bp upstream of the HL46e gene and a putative terminator sequence localized downstream from the HL30 gene. An equivalent to this HL46e/HL30 operon is apparently not present in Escherichia coli.

Amino Acid Sequence↗
PubMed1990

Amino acid sequences of the ribosomal proteins HL30 and HmaL5 from the archaebacterium Halobacterium marismortui.

The complete amino acid sequences of the ribosomal proteins HL30 and HmaL5 from the archaebacterium Halobacterium marismortui were determined. Protein HL30 was found to be acetylated at its N-terminal amino acid and shows homology to the eukaryotic ribosomal proteins YL34 from yeast and RL31 from rat. Protein HmaL5 was homologous to the protein L5 from Escherichia coli and Bacillus stearothermophilus as well as to YL16 from yeast. HmaL5 shows more similarities to its eukaryotic counterpart than to eubacterial ones.

Amino Acid Sequence↗
PubMed1988

Functional comparison of DCCD-sensitive Na+/H+ antiporter in Halobacterium halobium with monensin.

Membrane vesicles from Halobacterium halobium create a large, inside negative membrane potential (delta psi) and small, inside alkaline pH gradient (delta pH) by illumination in 3 M NaCl. delta psi was the major component of a proton electrochemical potential (delta microH+) over a pH range from 5 to 8. After DCCD treatment of the vesicles, delta psi was replaced by delta pH due to the inhibition of the intrinsic delta pH----delta psi transformation process: delta psi formation in light is markedly retarded and an inversely large delta pH is established at these pHs. DCCD-caused changes in delta psi and delta pH were completely restored to the control level by the addition of monensin, an electroneutral Na+/H+ exchanger. The ratio of DCCD-caused change in delta pH and delta psi was identical to that of monensin-recovered delta psi and delta pH. The delta psi/delta pH ratio was approximately 0.8, that is, 100 mV of delta pH was transformed into 78 mV of delta psi. The present results indicate that the intrinsic activity of the DCCD-sensitive delta pH----delta psi transformation is mediated by an electroneutral Na+/H+ exchange.

Biological Transport, Active↗
PubMed1991

Primary structures of ribosomal proteins from the archaebacterium Halobacterium marismortui and the eubacterium Bacillus stearothermophilus.

Approximately 40 ribosomal proteins from each Halobacterium marismortui and Bacillus stearothermophilus have been sequenced either by direct protein sequence analysis or by DNA sequence analysis of the appropriate genes. The comparison of the amino acid sequences from the archaebacterium H marismortui with the available ribosomal proteins from the eubacterial and eukaryotic kingdoms revealed four different groups of proteins: 24 proteins are related to both eubacterial as well as eukaryotic proteins. Eleven proteins are exclusively related to eukaryotic counterparts. For three proteins only eubacterial relatives-and for another three proteins no counterpart-could be found. The similarities of the halobacterial ribosomal proteins are in general somewhat higher to their eukaryotic than to their eubacterial counterparts. The comparison of B stearothermophilus proteins with their E coli homologues showed that the proteins evolved at different rates. Some proteins are highly conserved with 64-76% identity, others are poorly conserved with only 25-34% identical amino acid residues.

Amino Acid Sequence↗
PubMed1996

NAD-glutamate dehydrogenase from Halobacterium halobium: inhibition and activation by TCA intermediates and amino acids.

A variety of metabolites have been found to elicit a form of inhibition or activation on an NAD-specific glutamate dehydrogenase (NAD-GDH, EC 1.4.1.2) from Halobacterium halobium. The purified halophilic enzyme was tested with several compounds known to be allosteric modifiers of mammalian glutamate dehydrogenases to determine their effects on enzyme activity. GTP, ATP, ADP and AMP did not affect the enzyme, so these effectors of bovine glutamate dehydrogenase do not play a role in the regulation of the halophilic enzyme. However, the halophilic enzyme was subject to strong inhibition by TCA intermediates. When measuring the initial rate of the reaction, the oxidative deamination of L-glutamate was inhibited by TCA metabolites such as: fumarate, oxalacetate, succinate and malate; by substrate analogues such as: NADP+, D-glutamate and glutarate; and by dicarboxylic compounds such as adipate. On the other hand, all the amino acids tested were activators of this enzyme, except the D-isomer of the substrate L-glutamate that acted as an inhibitor. The relative effectiveness of each inhibitor or activator (Ki or Ka values) was correlated with the dipole moment (mu), HOMO and LUMO molecular orbital energies, optimal distance between two carboxyl groups, and hydrophobicity. Compounds with high dipole moment acted as good activators while compounds with low dipole moment were inhibitors. We have also found that the best activators were amino acids with no polar lateral chain.

Amino Acids↗
PubMed1988

Cloning and determination of the nucleotide sequence of the Mn-containing superoxide dismutase gene from Halobacterium halobium.

A group of synthetic 17-mer oligodeoxynucleotides (oligos) was constructed to correspond to a sequence of amino acids situated near the N terminus of the manganese-containing superoxide dismutase (Mn-SOD) purified from the halophilic bacterium, Halobacterium halobium. A cosmid library of a Sau3AI partial digest of halobium DNA, cloned into the BamHI site of pHC79, was probed with the radiolabeled oligos. Cosmid DNA was purified from the clone that showed hybridization at the highest stringency. A 1.8-kb PstI fragment of this DNA which hybridized the probes was subcloned into bacteriophage M13 and transfected into Escherichia coli JM101. The entire insert containing a 600-bp sequence coding for Mn-SOD and its 5'- and 3'-flanking regions was sequenced. The derived amino acid sequence of the structural gene showed a similarity to other manganese and iron-containing SODs in normally conserved regions.

Amino Acid Sequence↗