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Biomedical subjects

V Norris

Publications and source records attributed to V Norris.

At least 37 records · Page 2Linked to original sources
PubMed1998

Protein phosphorylation in Escherichia coli L. form NC-7.

Wall-less L-forms of Escherichia coli constitute an interesting, and relatively underused, model system for numerous studies of bacterial physiology including the cell cycle, intracellular structure and protein phosphorylation. Total extracts of the L-form revealed a pattern of protein phosphorylation similar to that of an enteropathogenic strain but very different from its parental K-12 strain. In particular, the L-form extract revealed phosphorylation on tyrosine of a protein important in pathogenesis, TypA, and calcium-specific phosphorylation of a 40 kDa protein. Two new phosphoproteins were identified in the L-form as the DNA-binding protein Dps, and YfiD, a protein of 14 kDa with homology to pyruvate formate-lyase and a region containing a tRNA cluster in bacteriophage T5.

Amino Acid Sequence↗
PubMed1997

The universal stress protein, UspA, of Escherichia coli is phosphorylated in response to stasis.

Transcriptional induction of the uspA gene of Escherichia coli occurs whenever conditions cause growth arrest and cells deficient in UspA survive poorly in stationary phase. We demonstrate that the product of uspA is a serine and threonine phosphoprotein. In vivo, three isoforms of UspA were detected, two of which were phosphorylated as determined by alkaline phosphatase treatment; in vitro, phosphorylation with [gamma-32P]ATP yielded two radioactive UspA isoforms. The phosphorylated isoforms were barely visible in growing cells but one increased during starvation conditions causing growth arrest. This phosphorylation is dependent on the o591 gene, which encodes an autophosphorylating tyrosine phosphoprotein and which is involved in the synthesis or modification of six other proteins. In vitro, UspA undergoes a rapid and dynamic autophosphorylation, as shown by chase experiments with GTP or ATP as phosphate donors.

Amino Acid Sequence↗
PubMed1997

Antiviruses as therapeutic agents: a mathematical analysis of their potential.

Antiviruses are designed to inhibit virus replication and arrest infections. A particular antivirus derives from a specific virus, on which it depends for propagation. Antiviruses have a natural equivalent in defective interfering particles (DIPs). To obtain design criteria for antiviruses, antivirus therapies for treating virus infections are modelled by a system of equations with continuous dynamics. The results reveal that such therapies can eliminate viruses given either a large but achievable inoculum of antivirus or an outcompeting advantage to the antivirus. Since such therapies are relatively insensitive to many parameters of infections, they may be applicable to many viral diseases.

Biotechnology↗
PubMed1997

Artefactual cleavage of E coli H-NS by OmpT.

In the bacterium Escherichia coli, H-NS-(H1, H1a) is a heat-stable protein with a molecular mass of 15.5 kDa involved in nucleoid organisation and gene regulation linked to certain signal transduction pathways. We have shown that, following addition of preparations of everted inner membrane vesicles, heat-stable cleavage products of approximately 10 kDa of H-NS are formed in vitro from newly synthesised, radio-labelled H-NS and from purified H-NS. The 15.5 kDa protein and its cleavage products were also recovered from a minicell system. These results raised the possibility that cleavage of H-NS is physiologically significant. However, the cleavage of H-NS observed appears to occur during cell breakage and to depend on the method of protein extraction and the presence of the outer membrane protease, OmpT. Nevertheless, the results indicate that H-NS may contain at least two separate domains with cleavage occurring between these domains at a preferred OmpT site. Failure to take account of H-NS cleavage in sample preparation and analysis can lead to serious underestimation of H-NS levels.

Artifacts↗
PubMed1997

Hypothesis: the meeting place model for prion disease.

Prions are responsible for spongiform diseases such as scrapie and bovine spongiform encephalopathy. It is now generally accepted that the disease mechanism involves the conversion from the normal form, PrPC, to the pathogenic form, PrPSc, and that this isoform is infectious. In the case of scrapie, 15 different forms of the disease have been described and some of these different phenotypes can be conferred by infectious prions that are themselves encoded by normal genes. We propose here that a prion with an altered structure has a correspondingly altered preference for lipids; this altered preference creates a proteolipid domain containing different lipids and other factors such as chaperonins and enzymes responsible for post-translational modifications. Normal prions associated with this abnormal domain adopt the conformation dictated by its lipidic composition (and by the other factors present) and so acquire the lipidic preference of the original pathogenic prions. These transformed prions could then create new proteolipid domains. This process may be considered as semi-conservative replication in which prion and lipids are analogous to the Watson and Crick strands and the proteolipid domain to the double helix itself.

Animals↗
PubMed1996

Elements of a unifying theory of biology.

To discover a unifying theory of biology, it is necessary first to believe in its existence and second to seek its elements. Such a theory would explain the regulation of the cell cycle, differentiation and the origin of life. Some elements of the theory may be obtained by considering both eukaryotic and prokaryotic cell cycles. These elements include cytoskeletal proteins, calcium, cyclins, protein kinase C, phosphorylation, transcriptional sensing, autocatalytic gene expression and the physical properties of lipids. Other more exotic candidate elements include the dynamic enzoskeleton, ATP generation, mechanotransduction, the piezoelectric effect and resonance. Bringing these disparate elements together--and discovering others--will require extensive collaborations between specialists from different sciences. This can only be achieved within the context of an integrated approach to biology.

Animals↗
PubMed1996

The Escherichia coli enzoskeleton.

The nature of the structure of the bacterial cell is becoming clearer. The envelope contains periseptal annuli, a discontinuous periplasm and adhesion sites, whilst the cytoplasmic membrane is probably organized into distinct proteolipid domains by the coupled transcription-translation-insertion (transertion) of membrane proteins. The structure of the nucleoid is determined by proteins which self-associate and by attachment to membrane, which is achieved in part by transertion. Metabolic pathways form multi-enzyme complexes which channel substrates and which connect membranes and nucleic acids to create the extensive, cross-linked, intracellular structure we term the 'enzoskeleton'. This enzoskeleton includes eukaryotic-like cytoskeletal structures and elements such as the MukB and FtsZ proteins. We propose that the enzoskeleton is regulated by calcium and by protein phosphorylation during adaptation to different environments and during the cell cycle.

Actins↗
PubMed1995

Autocatalytic gene expression occurs via transertion and membrane domain formation and underlies differentiation in bacteria: a model.

When bacteria contain two chromosomes, two or more copies of the same gene are present in the same cytoplasm and, if these copies are subject to negative regulation in trans and positive (autocatalytic) regulation in cis, one copy will be expressed at the expense of the other copy(ies). This autocatalytic process depends on the coupled transcription, or translation and insertion of nascent proteins into the membrane, or transertion. Transertion is responsible for looping genes out of the nucleoid and increasing their accessibility to transcription factors. Transertion of proteins with lipid preferences creates proteolipid domains in the membrane. These domains fuse to give two types of large domains, each associated with the expression of a particular set of genes. These large domains organize kinases, proteases and transcription factors and result in the expression of one set of genes encoding proteins with common lipid preferences from one chromosome and expression of a different set from the other. These intracellular differences underlie the production of different progeny by cell division that follows, for example, reception of extracellular signals, and that constitutes differentiation in bacteria.

Bacterial Proteins↗
PubMed1995

Characterization of eukaryotic-like kinase activity in Escherichia coli using the gene-protein database.

The gene-protein database was used to obtain the two-dimensional polyacrylamide gel coordinates of proteins phosphorylated in extracts of Escherichia coli including those phosphorylated by eukaryotic-like kinase activities. These suggest that the phosphoproteins correspond to, or co-migrate with, the product of an open reading frame at 1.3 min (Orf80), Enzyme 1 of the phosphoenolpyruvate-dependent phosphotransferase system (PtsI), the tRNA synthetase for histidine (HisS), and proteins involved in the response to carbon starvation and quinone treatment.

Bacterial Proteins↗
PubMed1995

Relationships between proteasomes and RNA.

The 20S proteasome (prosome) is a highly organized multi-protein complex with approximate molecular weight of about 700 kDa. Whilst the role of the proteasome in the processing and turnover of cellular proteins is becoming clearer, its relationship with RNA remains obscure. Over the last decade the possibility of association of proteasomes with specific RNAs or mRNPs have been particularly controversial. Proteasomes were reported to inhibit translation of viral mRNAs and to be tightly associated with RNase activity. It is possible that proteasomes are also involved in cellular RNA breakdown and RNA processing like prokaryotic RNase E.

Animals↗
PubMed1995

Identification of phosphoproteins in Escherichia coli.

The substrates of ion- and lipid-stimulated protein kinase activity in extracts of Escherichia coli were purified by chromatography. Subsequent N-terminal sequencing suggests that these substrates include the following: a novel 80 kDa protein co-purifying with RNA polymerase but partially homologous to elongation factor G; a protein with an apparent molecular weight of 65 kDa identified as the ribosomal protein S1; and a 32 kDa protein identified as succinyl CoA synthetase, a key enzyme in the tricarboxylic acid cycle. The phosphorylation of these three proteins was markedly stimulated by the addition of manganese, and occurred on threonine, serine or tyrosine residues as indicated by the stability of the phosphoresidues during acid treatment. In addition, a calcium-stimulated protein of 70 kDa was identified as the heat-shock protein DnaK, and a 17 kDa lipid-stimulated phosphoprotein as nucleotide diphosphate kinase.

Adenosine Triphosphate↗
PubMed1995

Hypothesis: chromosome separation in Escherichia coli involves autocatalytic gene expression, transertion and membrane-domain formation.

To explain how daughter chromosomes are separated into discrete nucleoids and why chromosomes are partitioned with pole preferences, I propose that differential gene expression occurs during DNA replication in Escherichia coli. This differential gene expression means that the daughter chromosomes have different patterns of gene expression and that cell division is not a simple process of binary fission. Differential gene expression arises from autocatalytic gene expression and creates a separate proteolipid domain around each developing chromosome via the coupled transcription-translation-insertion of proteins into membranes (transertion). As these domains are immiscible, daughter chromosomes are simultaneously replicated and separated into discrete nucleoids. I also propose that the partitioning relationship between chromosome age and cell age arises because the poles of cells have a proteolipid composition that favours transertion from one nucleoid rather than from the other. This hypothesis forms part of an ensemble of related hypotheses which attempt to explain cell division, differentiation and wall growth in bacteria in terms of the physical properties and interactions of the principal constituents of cells.

Cell Division↗
PubMed1994

Cell cycle control: prokaryotic solutions to eukaryotic problems?

Regulation of the eukaryotic cell cycle involves calcium- and lipid-stimulated kinases acting on cytoskeletal structures; there are two principal reasons for supposing that the regulation of the prokaryotic cell cycle may be fundamentally the same. First, evidence for their fundamental difference is still missing and, second, evidence for prokaryotic homologues of eukaryotic cell cycle proteins is accumulating. Such proteins include those involved in calcium regulation, such as calmodulin and calcium-dependent kinases, and those involved in lipid regulation, such as protein kinase C. Proteins identified as candidates for cytoskeletal elements now include MukB, a putative contractile protein responsible for chromosome segregation, and FtsZ, the key constituent of the "cytokinetic" ring. These similarities allow the application of powerful prokaryotic model systems to one of biology's most profound, complex and urgent problems: the nature of the regulation of the eukaryotic cell cycle.

Animals↗