bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fnr Is Required for NifL-Dependent Oxygen Control of
nif
Gene Expression in
Klebsiella pneumoniae
Authors: Grabbe Roman , Klopprogge Kai , Schmitz Ruth A. 
Published: July 2002

ABSTRACT

In
Klebsiella pneumoniae,
NifA-dependent transcription of nitrogen fixation (
nif
) genes is inhibited by NifL in response to molecular oxygen and combined nitrogen. We recently showed that
K. pneumoniae
NifL is a flavoprotein, which apparently senses oxygen through a redox-sensitive, conformational change. We have now studied the oxygen regulation of NifL activity in
Escherichia coli
and
K. pneumoniae
strains by monitoring its inhibition of NifA-mediated expression of
K. pneumoniae
ø(
nifH
′
-
′
lacZ
) fusions in different genetic backgrounds. Strains of both organisms carrying
fnr
null mutations failed to release NifL inhibition of NifA transcriptional activity under oxygen limitation:
nif
induction was similar to the induction under aerobic conditions. When the transcriptional regulator Fnr was synthesized from a plasmid, it was able to complement, i.e., to relieve NifL inhibition in the
fnr
mutant backgrounds. Hence, Fnr appears to be involved, directly or indirectly, in NifL-dependent oxygen regulation of
nif
gene expression in
K. pneumoniae
. The data indicate that in the absence of Fnr, NifL apparently does not receive the signal for anaerobiosis. We therefore hypothesize that in the absence of oxygen, Fnr, as the primary oxygen sensor, activates transcription of a gene or genes whose product or products function to relieve NifL inhibition by reducing the flavin adenine dinucleotide cofactor under oxygen-limiting conditions.
Drosophila
as a Model Host for
Pseudomonas aeruginosa
Infection
Authors: D'Argenio David A. , Gallagher Larry A. , Berg Celeste A. , Manoil Colin 
Published: July 2002

ABSTRACT

Using the fruit fly
Drosophila melanogaster
as model host, we have identified mutants of the bacterium
Pseudomonas aeruginosa
with reduced virulence. Strikingly, all strains strongly impaired in fly killing also lacked twitching motility; most such strains had a mutation in
pilGHIJKL chpABCDE
, a gene cluster known to be required for twitching motility and potentially encoding a signal transduction system. The
pil chp
genes appear to control the expression of additional virulence factors, however, since the wild-type fly-killing phenotype of a subset of mutants isolated on the basis of their compact colony morphology indicated that twitching motility itself was not required for full virulence in the fly.
Expression of Individual Copies of
Methylococcus capsulatus
Bath Particulate Methane Monooxygenase Genes
Authors: Stolyar Sergei , Franke Marion , Lidstrom Mary E. 
Published: July 2002

ABSTRACT

The expression of the two gene clusters encoding the particulate methane monooxygenase (pMMO) in
Methylococcus capsulatus
Bath was assessed by analysis of transcripts and by use of chromosomal gene fusions. The results suggest that the two clusters are functionally redundant but that relative expression alters depending on the copper levels available for growth.
Characterization of Interactions between the Transcriptional Repressor PhlF and Its Binding Site at the
phlA
Promoter in
Pseudomonas fluorescens
F113
Authors: Abbas Abdelhamid , Morrissey John P. , Marquez Pilar Carnicero , Sheehan Michelle M. , Delany Isabel R. , O'Gara Fergal 
Published: July 2002

ABSTRACT

The
phlACBD
genes responsible for the biosynthesis of the antifungal metabolite 2,4-diacetylphloroglucinol (PHL) by the biocontrol strain
Pseudomonas fluorescens
F113 are regulated at the transcriptional level by the pathway-specific repressor PhlF. Strong evidence suggests that this regulation occurs mainly in the early logarithmic phase of growth. First, the expression of the
phlF
gene is relatively high between 3 and 13 h of growth and relatively low thereafter, with the
phlACBD
operon following an opposite expression profile. Second, the kinetics of PHL biosynthesis are specifically altered in the logarithmic phase in a
P. fluorescens
F113
phlF
mutant. The
phlA-phlF
intergenic region presents a complex organization in that
phlACBD
is transcribed from a σ
70
RNA polymerase-dependent promoter that is likely to overlap the promoter of the divergently transcribed
phlF
gene. The repression by PhlF is due to its interaction with an inverted repeated sequence,
phO
, located downstream of the
phlA
transcriptional start site. Cross-linking experiments indicate that PhlF can dimerize in solution, and thus PhlF may bind
phO
as a dimer or higher-order complex. Furthermore, it is now demonstrated that certain regulators of PHL synthesis act by modulating PhlF binding to
phO
. PHL, which has previously been shown to be an autoinducer of PHL biosynthesis, interacts with PhlF to destabilize the PhlF-
phO
complex. Conversely, the PhlF-
phO
complex is stabilized by the presence of salicylate, which has been shown to be an inhibitor of
phlA
expression.
The Type IV Pilus Assembly Complex: Biogenic Interactions among the Bundle-Forming Pilus Proteins of Enteropathogenic
Escherichia coli
Authors: Ramer Sandra W. , Schoolnik Gary K. , Wu Cheng-Yen , Hwang Jaiweon , Schmidt Sarah A. , Bieber David 
Published: July 2002

ABSTRACT

Production of type IV bundle-forming pili (BFP) by enteropathogenic
Escherichia coli
(EPEC) requires the protein products of 12 genes of the 14-gene
bfp
operon. Antisera against each of these proteins were used to demonstrate that in-frame deletion of individual genes within the operon reduces the abundance of other
bfp
operon-encoded proteins. This result was demonstrated not to be due to downstream polar effects of the mutations but rather was taken as evidence for protein-protein interactions and their role in the stabilization of the BFP assembly complex. These data, combined with the results of cell compartment localization studies, suggest that pilus formation requires the presence of a topographically discrete assembly complex that is composed of BFP proteins in stoichiometric amounts. The assembly complex appears to consist of an inner membrane component containing three processed, pilin-like proteins, BfpI, -J, and -K, that localize with BfpE, -L, and -A (the major pilin subunit); an outer membrane, secretin-like component, BfpB and -G; and a periplasmic component composed of BfpU. Of these, only BfpL consistently localizes with both the inner and outer membranes and thus, together with BfpU, may articulate between the Bfp proteins in the inner membrane and outer membrane compartments.
Complete Polar Lipid Composition of
Thermoplasma acidophilum
HO-62 Determined by High-Performance Liquid Chromatography with Evaporative Light-Scattering Detection
Authors: Shimada Haruo , Nemoto Naoki , Shida Yasuo , Oshima Tairo , Yamagishi Akihiko 
Published: July 2002

ABSTRACT

Polar ether lipids of
Thermoplasma acidophilum
HO-62 were purified by high-performance liquid chromatography with an evaporative light-scattering detector. Structures of purified lipids were investigated by capillary gas chromatography, mass spectrometry, and nuclear magnetic resonance. Three types of ether lipids were found: phospholipids, glycolipids, and phosphoglycolipids. The two phospholipids had glycerophosphate as the phosphoester moiety. The seven glycolipids had different combinations of gulose, mannose, and glucose, which formed mono- or oligosaccharides. The eight phosphoglycolipids with two polar head groups contained glycerophosphate as the phosphoester moiety and gulose alone or gulose and mannose, which formed mono- or oligosaccharides, as the sugar moiety. Although gulose is an unusual sugar in nature, several glyco- and phosphoglycolipids contained gulose as one of the sugar moieties in
Thermoplasma acidophilum
. All the ether lipids had isopranoid chains of C
40
or C
20
with zero to three cyclopentane rings. The structures of these lipids including four new glycolipids and three new phosphoglycolipids were determined, and a glycosylation process for biosynthesis of these glycolipids was suggested.
Mutations in
Flavobacterium johnsoniae gldF
and
gldG
Disrupt Gliding Motility and Interfere with Membrane Localization of GldA
Authors: Hunnicutt David W. , Kempf Michael J. , McBride Mark J. 
Published: July 2002

ABSTRACT

Flavobacterium johnsoniae
moves rapidly over surfaces by a process known as gliding motility. The mechanism of this form of motility is not known. Four genes that are required for
F. johnsoniae
gliding motility,
gldA
,
gldB
,
gldD
, and
ftsX
, have recently been described. GldA is similar to the ATP-hydrolyzing components of ATP binding cassette (ABC) transporters. Tn
4351
mutagenesis was used to identify two additional genes,
gldF
and
gldG
, that are required for cell movement.
gldF
and
gldG
appear to constitute an operon, and a Tn
4351
insertion in
gldF
was polar on
gldG
. pMK314, which carries the entire
gldFG
region, restored motility to each of the
gldF
and
gldG
mutants. pMK321, which expresses GldG but not GldF, restored motility to each of the
gldG
mutants but did not complement the
gldF
mutant. GldF has six putative membrane-spanning segments and is similar in sequence to channel-forming components of ABC transporters. GldG is similar to putative accessory proteins of ABC transporters. It has two apparent membrane-spanning helices, one near the amino terminus and one near the carboxy terminus, and a large intervening loop that is predicted to reside in the periplasm. GldF and GldG are involved in membrane localization of GldA, suggesting that GldA, GldF, and GldG may interact to form a transporter.
F. johnsoniae gldA
is not closely linked to
gldFG
, but the
gldA
,
gldF
, and
gldG
homologs of the distantly related gliding bacterium
Cytophaga hutchinsonii
are arranged in what appears to be an operon. The exact roles of
F. johnsoniae
GldA, GldF, and GldG in gliding are not known. Sequence similarities of GldA to components of other ABC transporters suggest that the Gld transporter may be involved in export of some material to the periplasm, outer membrane, or beyond.
Quantitation of Porcine Cytomegalovirus in Pig Tissues by PCR
Authors: Fryer Jacqueline F. L. , Griffiths Paul D. , Fishman Jay A. , Emery Vincent C. , Clark Duncan A. 
Published: July 2002

ABSTRACT
A quantitative-competitive PCR for the quantification of porcine cytomegalovirus (PCMV) was developed. The virus was detected in a variety of pig organs (including potential xenotransplant donations), with viral loads ranging from <10 to 97 genome copies/μg of DNA. This assay will have significant utility for studying the activation and replication of PCMV and in swine models for allo- and xenotransplantation.
Streptococcal Meningitis Resulting from Contact with an Infected Horse
Authors: Downar James , Willey Barbara M. , Sutherland Jeffrey W. , Mathew Kelly , Low Donald E. 
Published: July 2002

ABSTRACT

We report a case of group C streptococcal meningitis in a woman with a history of close animal contact as well as head trauma as a result of a kick by a horse. Blood and cerebrospinal fluid cultures grew
Streptococcus equi
subsp.
zooepidemicus
, as did a throat culture taken from the colt that had kicked her 2 weeks prior to admission.
Highly Sensitive Assay for Human Herpesvirus 8 Antibodies That Uses a Multiple Antigenic Peptide Derived from Open Reading Frame K8.1
Authors: Lam Lee L. , Pau Chou-Pong , Dollard Sheila C. , Pellett Philip E. , Spira Thomas J. 
Published: July 2002

ABSTRACT
The immunodominant region of the human herpesvirus 8 (HHV-8), the antibody-binding site of glycoprotein K8.1A, was mapped to the N-terminal region by using overlapping peptides and a residue replacement method. The main epitope was located within residues 44 to 56 (GQVYQDWL----C). Based on this information, we developed an enzyme immunoassay to detect HHV-8 antibodies in human sera using a four-branch multiple antigenic peptide as the antigen. The sensitivity and specificity of the assay were 96 and 99.4%, respectively. This assay should be useful for population-based, epidemiological studies of HHV-8 infection.
The Human Immunodeficiency Virus Type 1 gp120 V2 Domain Mediates gp41-Independent Intersubunit Contacts
Authors: Center Rob J. , Earl Patricia L. , Lebowitz Jacob , Schuck Peter , Moss Bernard 
Published: July 2002

ABSTRACT
The envelope protein of human immunodeficiency virus type 1 HIV-1 undergoes proteolytic cleavage in the Golgi complex to produce subunits designated gp120 and gp41, which remain noncovalently associated. While gp41 has a well-characterized oligomeric structure, the maintenance of gp41-independent gp120 intersubunit contacts remains a contentious issue. Using recombinant vaccinia virus to achieve high-level expression of gp120 in mammalian cells combined with gel filtration analysis, we were able to isolate a discrete oligomeric form of gp120. Oligomerization of gp120 occurred intracellularly between 30 and 120 min after synthesis. Analysis by sedimentation equilibrium unequivocally identified the oligomeric species as a dimer. In order to identify the domains involved in the intersubunit contact, we expressed a series of gp120 proteins lacking various domains and assessed the effects of mutation on oligomeric structure. Deletion of the V1 or V3 loops had little effect on the relative amounts of monomer and dimer in comparison to wild-type gp120. In contrast, deletion of either all or part of the V2 loop drastically reduced dimer formation, indicating that this domain is required for intersubunit contact formation. Consistent with this, the V2 loop of the dimer was less accessible than that of the monomer to a specific monoclonal antibody. Previous studies have shown that while the V2 loop is not an absolute requirement for viral entry, the absence of this domain reduces viral resistance to neutralization by monoclonal antibodies or sera. We propose that the quaternary structure of gp120 may contribute to resistance to neutralization by limiting the exposure of conserved epitopes.
Identifying the Determinants in the Equatorial Domain of
Buchnera
GroEL Implicated in Binding
Potato Leafroll Virus
Authors: Hogenhout Saskia A. , van der Wilk Frank , Verbeek Martin , Goldbach Rob W. , van den Heuvel Johannes F. J. M. 
Published: July 2002

ABSTRACT

Luteoviruses avoid degradation in the hemolymph of their aphid vector by interacting with a GroEL homolog from the aphid's primary endosymbiotic bacterium (
Buchnera
sp.). Mutational analysis of GroEL from the primary endosymbiont of
Myzus persicae
(MpB GroEL) revealed that the amino acids mediating binding of
Potato leafroll virus
(PLRV;
Luteoviridae
) are located within residues 9 to 19 and 427 to 457 of the N-terminal and C-terminal regions, respectively, of the discontinuous equatorial domain. Virus overlay assays with a series of overlapping synthetic decameric peptides and their derivatives demonstrated that R13, K15, L17, and R18 of the N-terminal region and R441 and R445 of the C-terminal region of the equatorial domain of GroEL are critical for PLRV binding. Replacement of R441 and R445 by alanine in full-length MpB GroEL and in MpB GroEL deletion mutants reduced but did not abolish PLRV binding. Alanine substitution of either R13 or K15 eliminated the PLRV-binding capacity of the other and those of L17 and R18. In the predicted tertiary structure of GroEL, the determinants mediating virus binding are juxtaposed in the equatorial plain.
Isolation of Borna Disease Virus from Human Brain Tissue
Authors: Nakamura Yurie , Takahashi Hirokazu , Shoya Yuko , Nakaya Takaaki , Watanabe Makiko , Tomonaga Keizo , Iwahashi Kazuhiko , Ameno Kiyoshi , Momiyama Noriko , Taniyama Hiroyuka , Sata Tetsutaro , Kurata Takeshi , de la Torre Juan Carlos , Ikuta Kazuyoshi 
Published: July 2002

ABSTRACT
Serological and molecular epidemiological studies indicate that Borna disease virus (BDV) can infect humans and is possibly associated with certain neuropsychiatric disorders. We examined brain tissue collected at autopsy from four schizophrenic patients and two healthy controls for the presence of BDV markers in 12 different brain regions. BDV RNA and antigen was detected in four brain regions of a BDV-seropositive schizophrenic patient (P2) with a very recent (2 years) onset of disease. BDV markers exhibited a regionally localized distribution. BDV RNA was found in newborn Mongolian gerbils intracranially inoculated with homogenates from BDV-positive brain regions of P2. Human oligodendroglia (OL) cells inoculated with brain homogenates from BDV-positive gerbils allowed propagation and isolation of BDVHuP2br, a human brain-derived BDV. Virus isolation was also possible by transfection of Vero cells with ribonucleoprotein complexes prepared from BDV-positive human and gerbil brain tissues. BDVHuP2br was genetically closely related to but distinct from previously reported human- and animal-derived BDV sequences.
Rotavirus-Induced Structural and Functional Alterations in Tight Junctions of Polarized Intestinal Caco-2 Cell Monolayers
Authors: Obert Guillaume , Peiffer Isabelle , Servin Alain L. 
Published: July 2002

ABSTRACT

We provide here new insights into rotavirus (RRV) pathogenicity by showing that RRV infection promotes structural and functional injuries localized at the tight junctions (TJ) in the cell-cell junctional complex of cultured polarized human intestinal Caco-2 cells forming monolayers. RRV infection resulted in a progressive increase in the paracellular permeability to [
3
H]mannitol as a function of the time postinfection. We observed a disorganization of the TJ-associated protein occludin as a function of the time postinfection, whereas distribution of the zonula adherens associated E-cadherin was not affected. These structural and functional RRV-induced TJ injuries were not accompanied by alteration in cell and monolayer integrity, as assessed by the lack of change in transepithelial membrane resistance and lactate dehydrogenase release. Finally, using the stabilizer of actin filaments Jasplakinolide, we demonstrated that the RRV-induced structural and functional alterations in TJ are independent of the RRV-induced apical F-actin rearrangements.
Functional Analyses of the EBNA1 Origin DNA Binding Protein of Epstein-Barr Virus
Authors: Ceccarelli Derek F. J. , Frappier Lori 
Published: July 2002

ABSTRACT

The EBNA1 protein of Epstein-Barr virus (EBV) governs the replication and segregation of the viral episomes in latently infected cells and transactivates the expression of other EBV latency proteins through direct interactions with DNA sequences in the EBV latent origin of replication,
oriP
. To better understand how EBNA1 controls these processes, we have assessed the contribution of various EBNA1 sequences to its replication, segregation, and transactivation functions. Here we show that EBNA1 residues 325 to 376 are responsible for the transactivation activity of EBNA1. This region coincides with the DNA looping domain previously shown to mediate interactions at a distance between DNA-bound EBNA1 molecules. The same residues mediate DNA segregation but have no apparent role in DNA replication, indicating that the replication and transcription activation activities of EBNA1 are distinct. The acidic C-terminal tail of EBNA1 was not found to contribute to replication, transactivation, or segregation. We have also investigated the functional significance of two structural motifs within the DNA binding and dimerization domains of EBNA1, the proline loop and the WF motif. Although the amino acids in these motifs do not directly contact the DNA, both of these motifs were found to contribute to EBNA1 functions by increasing the DNA-binding ability of EBNA1. Mechanisms by which DNA binding is stimulated by these motifs are discussed.
Assembly of the Coronavirus Envelope: Homotypic Interactions between the M Proteins
Authors: de Haan Cornelis A. M. , Vennema Harry , Rottier Peter J. M. 
Published: July 2002

ABSTRACT
The viral membrane proteins M and E are the minimal requirements for the budding of coronavirus particles. Since the E protein occurs in particles only in trace amounts, the lateral interactions between the M proteins apparently generate the major driving force for envelope formation. By using coimmunoprecipitation and envelope incorporation assays, we provide extensive evidence for the existence of such M-M interactions. In addition, we determined which domains of the M protein are involved in this homotypic association, using a mutagenetic approach. Mutant M proteins which were not able to assemble into viruslike particles (VLPs) by themselves (C. A. M. de Haan, L. Kuo, P. S. Masters, H. Vennema, and P. J. M. Rottier, J. Virol. 72:6838–6850, 1998) were tested for the ability to associate with other M proteins and to be rescued into VLPs formed by assembly-competent M proteins. We found that M proteins lacking parts of the transmembrane cluster, of the amphipathic domain, or of the hydrophilic carboxy-terminal tail, or M proteins that had their luminal domain replaced by heterologous ectodomains, were still able to associate with assembly-competent M proteins, resulting in their coincorporation into VLPs. Only a mutant M protein in which all three transmembrane domains had been replaced lost this ability. The results indicate that M protein molecules interact with each other through multiple contact sites, particularly at the transmembrane level. Finally, we tested the stringency with which membrane proteins are selected for incorporation into the coronavirus envelope by probing the coassembly of some foreign proteins. The observed efficient exclusion from budding of the vesicular stomatitis virus G protein and the equine arteritis virus M protein indicates that envelope assembly is indeed a highly selective sorting process. The low but detectable incorporation of CD8 molecules, however, demonstrated that this process is not perfect.
Antiapoptotic Herpesvirus Bcl-2 Homologs Escape Caspase-Mediated Conversion to Proapoptotic Proteins
Authors: Bellows David S. , Chau B. Nelson , Lee Percy , Lazebnik Yuri , Burns William H. , Hardwick J. Marie 
Published: July 2002

ABSTRACT

The antiapoptotic Bcl-2 and Bcl-x
L
proteins of mammals are converted into potent proapoptotic factors when they are cleaved by caspases, a family of apoptosis-inducing proteases (E. H.-Y. Cheng, D. G. Kirsch, R. J. Clem, R. Ravi, M. B. Kastan, A. Bedi, K. Ueno, and J. M. Hardwick, Science 278:1966–1968, 1997; R. J. Clem, E. H.-Y. Cheng, C. L. Karp, D. G. Kirsch, K. Ueno, A. Takahashi, M. B. Kastan, D. E. Griffin, W. C. Earnshaw, M. A. Veliuona, and J. M. Hardwick, Proc. Natl. Acad. Sci. USA 95:554–559, 1998). Gamma herpesviruses also encode homologs of the Bcl-2 family. All tested herpesvirus Bcl-2 homologs possess antiapoptotic activity, including the more distantly related homologs encoded by murine gammaherpesvirus 68 (γHV68) and bovine herpesvirus 4 (BHV4), as described here. To determine if viral Bcl-2 proteins can be converted into death factors, similar to their cellular counterparts, five herpesvirus Bcl-2 homologs from five different viruses were tested for their susceptibility to caspases. Only the viral Bcl-2 protein encoded by γHV68 was susceptible to caspase digestion. However, unlike the caspase cleavage products of cellular Bcl-2, Bcl-x
L
, and Bid, which are potent inducers of apoptosis, the cleavage product of γHV68 Bcl-2 lacked proapoptotic activity. KSBcl-2, encoded by the Kaposi's sarcoma-associated herpesvirus, was the only viral Bcl-2 homolog that was capable of killing cells when expressed as an N-terminal truncation. However, because KSBcl-2 was not cleavable by caspases, the latent proapoptotic activity of KSBcl-2 apparently cannot be released. The Bcl-2 homologs encoded by herpesvirus saimiri, Epstein-Barr virus, and BHV4 were not cleaved by apoptotic cell extracts and did not possess latent proapoptotic activities. Thus, herpesvirus Bcl-2 homologs escape negative regulation by retaining their antiapoptotic activities and/or failing to be converted into proapoptotic proteins by caspases during programmed cell death.