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F Pfeifer

Publications and source records attributed to F Pfeifer.

43 records · Page 3Linked to original sources
PubMed1984

Characterization of insertions affecting the expression of the bacterio-opsin gene in Halobacterium halobium.

We have determined the sequence of the inverted repeats and duplicated target DNA of the halobacterial insertion elements ISH2 (520 bp), ISH23 (900 bp) and ISH24 (3000 bp) associated with bacterio-opsin (bop) mutants. ISH2 has a perfect 19 bp inverted repeat (3,5), while both ISH23 and ISH24 have imperfect inverted repeats of 29 bp and 14 bp respectively. ISH23 was shown to be highly homologous to ISH50 (6). Variable lengths of duplicated target DNA are found when ISH2 and ISH23 (ISH50) transpose into different sites. A 550 bp DNA insert ("ISH25") reverts the Bop mutation caused by ISH24. "ISH25" lacks typical structural features of a transposable element. "ISH25" and ISH24 are found adjacent to each other upstream of the bop gene. An identical arrangement of "ISH25" and ISH24 is found in the cccDNA of H. halobium NRC817. Comparative sequence analysis of both areas suggests that the translocation of "ISH25" to the bop gene region occurred by a recombination event.

Bacteriorhodopsins↗
PubMed1983

Bacterio-opsin mutants of Halobacterium halobium.

The bacterio-opsin (bop) gene of Halobacterium halobium R1 has been cloned with about 40 kilobases of flanking genomic sequence. The 40-kilobase segment is derived from the (G+C)-rich fraction of the chromosome and is not homologous to the major (pHH1) or minor endogenous covalently closed circular DNA species of H. halobium. A 5.1-kilobase Pst I fragment containing the bop gene was subcloned in pBR322 and a partial restriction map was determined. Defined restriction fragments of this clone were used as probes to analyze the defects associated with the bop gene in 12 bacterio-opsin mutants. Eleven out of 12 of the mutants examined had inserts ranging from 350 to 3,000 base pairs either in the bop gene or up to 1,400 base pairs upstream. The positions of the inserts were localized to four regions in the 5.1-kilobase genomic fragment: within the gene (one mutant), in a region that overlaps the 5' end of the gene (seven mutants), and in two different upstream regions (three mutants). Two revertants of the mutant with the most distal insert had an additional insert in the same region. The polar effects of these inserts are discussed in terms of inactivation of a regulatory gene or disruption of part of a coordinately expressed operon. Given the defined nature of the bop mRNA-i.e., it has a 5' leader sequence of three ribonucleotides-these observations indicate that the bop mRNA might be processed from a large mRNA transcript.

Journal Article↗
PubMed1981

Characterization of plasmids in halobacteria.

Extrachromosomal, covalently closed circular deoxyribonucleic acid has been isolated from different species of halobacteria. Three strains of Halobacterium halobium and one of Halobacterium cutirubrum, all of which synthesize purple membrane (Pum+) and bacterioruberin (Rub+), contain plasmids of different size which share extensive sequence homologies. One strain of Halobacterium salinarium, another one of Halobacterium capanicum, and two new Halobacterium isolates from Tunisia, which are also Pum+ Rub+, do not harbor covalently closed circular deoxyribonucleic acid but contain sequences, presumably integrated into the chromosome, which are similar if not identical to those of pHH1, i.e., the plasmid originally isolated from H. halobium. Three other halophilic strains, Halobacterium trapanicum, Halobacterium volcanii, and a new isolate from Israel, do not carry pHH1-like sequences. These strains are, by morphological and physiological criteria, different from the others examined and harbor plasmids unrelated to pHH1.

Base Sequence↗
PubMed1981

Genetic variability in Halobacterium halobium.

Halobacterium halobium exhibits an extraordinary degree of spontaneous variability. Mutants which are defective in the formation of gas vacuoles (vac) arise at a frequency of 10(-2). Other easily detectable phenotypes, like the synthesis of bacterioruberin (Rub) or the synthesis of retinal (Ret) and bacterio-opsin (Ops), the two components which form the purple membrane (Pum) of H. halobium, are lost at a frequency of about 10(-4). With the same frequency a mutant type appears which exhibits an extremely high variability in these phenotypes. With the exception of the ret mutants, all spontaneously arising mutants show alterations, i.e., insertions, rearrangements, or deletions, in the plasmid pHH1. It appears that the introduction of one insertion into pHH1 triggers further insertions, which makes the identification of relationships between phenotypic and genotypic alterations rather difficult. From the analysis of a large number of spontaneous vac mutants and their vac+ revertants it can be concluded that the formation of the gas vacuoles is determined or controlled by plasmid genes. No such conclusion is yet possible for the rub mutants, although all mutants of this type so far analyzed exhibit a defined insertion. pum mutants which have lost the capability of forming bacterio-opsin carry insertions in the plasmid which are distributed over a rather large region of the plasmid. No strains of H. halobium could be obtained which had lost plasmid pHH1 completely.

DNA Transposable Elements↗
PubMed1977

Transposition and insertion of intact, deleted and enlarged ampicillin transposon Tn3 from mini-R1 (Rsc) plasmids into transfer factors.

The miniR1-(Rsc)-plasmids which derive from the copy mutant R1drd-19B2 (pKN102) are non-conjugative extrachromosomal elements which can not be co-transferred by various transfer factors to recipient strains under standard mating conditions. The attempts to mobilize Rsc11 by F'lac lead to transconjugants carrying F'lac::Tn3 with Tn3 mainly inserted into the lac operon. In addition it can be shown that Rsc11 can become inserted as a complete unit into the transfer factor giving rise to rather unstable recombinant intermediates. Dissociation of these intermediates may lead to alterations of the original plasmids. The Tn3 part of Rsc13 can be enlarged or deleted by in vitro manipulations. In vitro insertion of EcoRI-fragments into an EcoRI+ site of Tn3 leads to new transposable units which can be transposed to the RTF part of R1. This new genetic entity can be stably integrated into the chromosome of E. coli by integrative suppression of a dnaAts-mutation. Deletions at one end or the central region of Tn3 abolish the capability of transposition. However, the Rsc-plasmids containing the deleted Tn3 can still be inserted into the transfer factor as complete units. The resulting recombinants are unstable leading after dissociation in some cases to new plasmids with altered properties.

Ampicillin↗
PubMedDate not supplied

Lung retrieval from non-heart-beating donors: first experience with an innovative preservation strategy in a pig lung transplantation model.

OBJECTIVE: Lung transplantation is limited by the scarcity of donor organs. Lung retrieval from non-heart-beating donors (NHBD) might extend the donor pool and has been reported recently. However, no studies in NHBD exist using the novel approach of retrograde preservation with Perfadex solution. METHODS: Heparinized asystolic pigs (n = 5, 30-35 kg) were ventilated for 90 min. The lungs were retrogradely preserved with Perfadex solution and stored inflated at 4 degrees C for 3 h. Left lung transplantation in the recipient was followed by exclusion of the right lung. Results were compared to sham-operated animals. Oxygenation, hemodynamics and dynamic compliance were monitored for 4 h. Infiltration of polymorphonuclear cells (PMNs) and stereological quantification of alveolar edema was performed. Statistical analysis comprised Kruskal-Wallis and Mann-Whitney tests and ANOVA analysis with repeated measures. RESULTS: No mortality was observed. During preservation, continuous elimination of blood clots via the pulmonary artery venting site was observed. Oxygenation and compliance were similar between groups, but sham controls showed significantly lower pulmonary vascular resistance. Stereological quantification revealed higher volume fractions of intra-alveolar edema in NHBD grafts, while PMN infiltration was comparable to sham controls. CONCLUSIONS: Use of NHBD lungs results in excellent outcome after 90 min of warm ischemia followed by retrograde preservation with Perfadex solution. This novel approach can optimize lung preservation by eliminating clots from the pulmonary circulation and might clinically be considered in brain-dead organ donors who become hemodynamically unstable prior to organ harvest. Further trials with longer warm and cold ischemic periods are necessary to further elucidate this promising approach to donor pool expansion.

Animals↗