Definition of the binding specificity of the T7 bacteriophage primase by analysis of a protein binding microarray using a thermodynamic model

Protein binding microarrays (PBM), SELEX, RNAcompete and chromatin-immunoprecipitation have been intensively used to determine the specificity of nucleic acid binding proteins. While the specificity of proteins with pronounced sequence specificity is straightforward, the determination of the sequence specificity of proteins of modest sequence specificity is more difficult. In this work, an explorative data analysis workflow for nucleic acid binding data was developed that can be used by scientists that want to analyse their binding data. The workflow is based on a regressor realized in scikit-learn, the major machine learning module for the scripting language Python. The regressor is built on a thermodynamic model of nucleic acid binding and describes the sequence specificity with base- and position-specific energies. The regressor was used to determine the binding specificity of the T7 primase. For this, we reanalysed the binding data of the T7 primase obtained with a custom PBM. The binding specificity of the T7 primase agrees with the priming specificity (5'-GTC) and the template (5'-GGGTC) for the preferentially synthesized tetraribonucleotide primer (5'-pppACCC) but is more relaxed. The dominant contribution of two positions in the motif can be explained by the involvement of the initiating and elongating nucleotides for template binding.

Initial Primer Synthesis of a DNA Primase Monitored by Real-Time NMR Spectroscopy

Primases are crucial enzymes for DNA replication, as they synthesize a short primer required for initiating DNA replication. We herein present time-resolved nuclear magnetic resonance (NMR) spectroscopy in solution and in the solid state to study the initial dinucleotide formation reaction of archaeal pRN1 primase. Our findings show that the helix-bundle domain (HBD) of pRN1 primase prepares the two substrates and then hands them over to the catalytic domain to initiate the reaction. By using nucleotide triphosphate analogues, the reaction is substantially slowed down, allowing us to study the initial dinucleotide formation in real time. We show that the sedimented protein-DNA complex remains active in the solid-state NMR rotor and that time-resolved 31P-detected cross-polarization experiments allow monitoring the kinetics of dinucleotide formation. The kinetics in the sedimented protein sample are comparable to those determined by solution-state NMR. Protein conformational changes during primer synthesis are observed in time-resolved 1H-detected experiments at fast magic-angle spinning frequencies (100 kHz). A significant number of spectral changes cluster in the HBD pointing to the importance of the HBD for positioning the nucleotides and the dinucleotide.

The monomeric archaeal primase from Nanoarchaeum equitans harbours the features of heterodimeric archaeoeukaryotic primases and primes sequence-specifically

The marine thermophilic archaeon Nanoarchaeum equitans possesses a monomeric primase encompassing the conserved domains of the small catalytic and the large regulatory subunits of archaeoeukaryotic heterodimeric primases in one protein chain. The recombinant protein primes on templates containing a triplet with a central thymidine, thus displaying a pronounced sequence specificity typically observed with bacterial type primases only. The N. equitans primase (NEQ395) is a highly active primase enzyme synthesizing short RNA primers. Termination occurs preferentially at about nine nucleotides, as determined by HPLC analysis and confirmed with mass spectrometry. Possibly, the compact monomeric primase NEQ395 represents the minimal archaeoeukaryotic primase and could serve as a functional and structural model of the heterodimeric archaeoeukaryotic primases, whose study is hindered by engagement in protein assemblies and rather low activity.

Efficient colonic drug delivery in domestic pigs employing a tablet formulation with dual control concept

Efficient and reproducible colonic drug delivery remains elusive. The aim of this study was to demonstrate specific colonic delivery in vivo in domestic pigs with a novel tablet formulation based on a dual release control concept using 5-aminosalicylic acid (5-ASA) and caffeine as drug substances. The developed controlled colonic release (CCR) tablet formulation employs a pH-sensitive coating based on Eudragit® FS 30 D to prevent drug release in the upper gastrointestinal tract, and a xyloglucan-based matrix to inhibit drug release after coating removal in the small intestine and to allow microbiome-triggered drug release by enzymatic action in the colon. CCR tablets were administered to domestic pigs and plasma concentration data was analyzed by physiologically based pharmacokinetic modeling to estimate absorbed amounts from small and large intestine and in vivo drug release rates by model-dependent deconvolution using immediate release (IR) tablets and intravenous solutions as reference. Peak concentration times (t_max) and values (c_max) of CCR 5-ASA and caffeine tablets indicated strongly delayed drug absorption and the deduced absorbed amount as a function of time confirmed absorption overwhelmingly from the large intestine. The microbially cleaved marker molecule sulfasalazine administered alone or together with caffeine in CCR tablets reported, in combination with telemetry measurements, gastrointestinal transit times and site of absorption. Drug release from CCR tablets was inferred to take place predominantly at the site of absorption at a release rate of caffeine that was much larger in the colon than in the small intestine indicating enzymatically triggered release by the colonic microbiome. Xyloglucanase activity in rectal and cecal samples was consistent with release data and compound recovery in fecal droppings was consistent with 5-ASA bioavailability. The results provide evidence that the developed formulation can prevent premature drug release and provide targeted colonic drug delivery. Clinical relevance based on the comparability between pig and man is discussed.

Tablet formulation with dual control concept for efficient colonic drug delivery

Aim of this study was to develop a tablet formulation for targeted colonic drug release by implementing two control mechanisms: A pH-sensitive coating layer based on Eudragit® FS 30 D to prevent drug release in the upper gastrointestinal tract, combined with a matrix based on plant-derived polysaccharide xyloglucan to inhibit drug release after coating removal in the small intestine and to allow microbiome triggered drug release in the colon. In vitro dissolution tests simulated the passage through the entire gastrointestinal tract with a four-stage protocol, including microbial xyloglucanase addition in physiologically relevant concentrations as microbiome surrogate to the colonic dissolution medium. Matrix erosion was monitored in parallel to drug release by measurement of reducing sugar equivalents resulting from xyloglucan hydrolysis. Limited drug release in gastric and small intestinal test stages and predominant release in the colonic stage was achieved. The xyloglucan matrix controlled drug release after dissolution of the enteric coating through the formation of a gummy polysaccharide layer at the tablet surface. Matrix degradation was dependent on enzyme concentration in the colonic medium and significantly accelerated drug release resulting in erosion-controlled release process. Drug release at physiologically relevant enzyme concentration was completed within the bounds of colonic transit time. The dual control concept was applicable to two drug substances with different solubility, providing similar release rates in colonic environment containing xyloglucanase. Drug solubility mechanistically affected release, with diffusion of caffeine, but not of 5-ASA, contributing to the overall release rate out of the matrix tablet.

Stringent Primer Termination by an Archaeo-Eukaryotic DNA Primase

Priming of single stranded templates is essential for DNA replication. In recent years, significant progress was made in understanding how DNA primase fulfils this fundamental function, particularly with regard to the initiation. Equally intriguing is the unique property of archeao-eukaryotic primases to terminate primer formation at a well-defined unit length. The apparent ability to “count” the number of bases incorporated prior to primer release is not well understood, different mechanisms having been proposed for different species. We report a mechanistic investigation of primer termination by the pRN1 primase from Sulfolobus islandicus. Using an HPLC-based assay we determined structural features of the primer 5′-end that are required for consistent termination. Mutations within the unstructured linker connecting the catalytic domain to the template binding domain allowed us to assess the effect of altered linker length and flexibility on primer termination.

Stable and selective permeable hydrogel microcapsules for high-throughput cell cultivation and enzymatic analysis

BACKGROUND

Miniaturization of biochemical reaction volumes within artificial microcompartments has been the key driver for directed evolution of several catalysts in the past two decades. Typically, single cells are co-compartmentalized within water-in-oil emulsion droplets with a fluorogenic substrate whose conversion allows identification of catalysts with improved performance. However, emulsion droplet-based technologies prevent cell proliferation to high density and preclude the feasibility of biochemical reactions that require the exchange of small molecule substrates. Here, we report on the development of a high-throughput screening method that addresses these shortcomings and that relies on a novel selective permeable polymer hydrogel microcapsule.

RESULTS

Hollow-core polyelectrolyte-coated chitosan alginate microcapsules (HC-PCAMs) with selective permeability were successfully constructed by jet break-up and layer-by-layer (LBL) technology. We showed that HC-PCAMs serve as miniaturized vessels for single cell encapsulation, enabling cell growth to high density and cell lysis to generate monoclonal cell lysate compartments suitable for high-throughput analysis using a large particle sorter (COPAS). The feasibility of using HC-PCAMs as reaction compartments which exchange small molecule substrates was demonstrated using the transpeptidation reaction catalyzed by the bond-forming enzyme sortase F from P. acnes. The polyelectrolyte shell surrounding microcapsules allowed a fluorescently labelled peptide substrate to enter the microcapsule and take part in the transpeptidation reaction catalyzed by the intracellularly expressed sortase enzyme retained within the capsule upon cell lysis. The specific retention of fluorescent transpeptidation products inside microcapsules enabled the sortase activity to be linked with a fluorescent readout and allowed clear separation of microcapsules expressing the wild type SrtF from those expressing the inactive variant.

CONCLUSION

A novel polymer hydrogel microcapsule-based method, which allows for high-throughput analysis based on encapsulation of single cells has been developed. The method has been validated for the transpeptidation activity of sortase enzymes and represents a powerful tool for screening of libraries of sortases, other bond-forming enzymes, as well as of binding affinities in directed evolution experiments. Moreover, selective permeable microcapsules encapsulating microcolonies provide a new and efficient means for preparing novel caged biocatalyst and biosensor agents.

Recent advances in understanding bacterial and archaeoeukaryotic primases

DNA replication in all forms of life relies upon the initiation of synthesis on a single strand template by formation of a short oligonucleotide primer, which is subsequently elongated by DNA polymerases. Two structurally distinct classes of enzymes have evolved to perform this function, namely the bacterial DnaG-type primases and the Archaeal and Eukaryotic primases (AEP). Structural and mechanistic insights have provided a clear understanding of the role of the different domains of these enzymes in the context of the replisome and recent work sheds light upon primase-substrate interactions. We herein review the emerging picture of the primase mechanism on the basis of the structural knowledge obtained to date and propose future directions of this essential aspect of DNA replication.

A Small Helical Bundle Prepares Primer Synthesis by Binding Two Nucleotides that Enhance Sequence-Specific Recognition of the DNA Template

Primases have a fundamental role in DNA replication. They synthesize a primer that is then extended by DNA polymerases. Archaeoeukaryotic primases require for synthesis a catalytic and an accessory domain, the exact contribution of the latter being unresolved. For the pRN1 archaeal primase, this domain is a 115-amino acid helix bundle domain (HBD). Our structural investigations of this small HBD by liquid- and solid-state nuclear magnetic resonance (NMR) revealed that only the HBD binds the DNA template. DNA binding becomes sequence-specific after a major allosteric change in the HBD, triggered by the binding of two nucleotide triphosphates. The spatial proximity of the two nucleotides and the DNA template in the quaternary structure of the HBD strongly suggests that this small domain brings together the substrates to prepare the first catalytic step of primer synthesis. This efficient mechanism is likely general for all archaeoeukaryotic primases.

Evidence-Based Clinical Use of Nanoscale Extracellular Vesicles in Nanomedicine

Recent research has demonstrated that all body fluids assessed contain substantial amounts of vesicles that range in size from 30 to 1000 nm and that are surrounded by phospholipid membranes containing different membrane microdomains such as lipid rafts and caveolae. The most prominent representatives of these so-called extracellular vesicles (EVs) are nanosized exosomes (70-150 nm), which are derivatives of the endosomal system, and microvesicles (100-1000 nm), which are produced by outward budding of the plasma membrane. Nanosized EVs are released by almost all cell types and mediate targeted intercellular communication under physiological and pathophysiological conditions. Containing cell-type-specific signatures, EVs have been proposed as biomarkers in a variety of diseases. Furthermore, according to their physical functions, EVs of selected cell types have been used as therapeutic agents in immune therapy, vaccination trials, regenerative medicine, and drug delivery. Undoubtedly, the rapidly emerging field of basic and applied EV research will significantly influence the biomedicinal landscape in the future. In this Perspective, we, a network of European scientists from clinical, academic, and industry settings collaborating through the H2020 European Cooperation in Science and Technology (COST) program European Network on Microvesicles and Exosomes in Health and Disease (ME-HAD), demonstrate the high potential of nanosized EVs for both diagnostic and therapeutic (i.e., theranostic) areas of nanomedicine.

Biological properties of extracellular vesicles and their physiological functions

In the past decade, extracellular vesicles (EVs) have been recognized as potent vehicles of intercellular communication, both in prokaryotes and eukaryotes. This is due to their capacity to transfer proteins, lipids and nucleic acids, thereby influencing various physiological and pathological functions of both recipient and parent cells. While intensive investigation has targeted the role of EVs in different pathological processes, for example, in cancer and autoimmune diseases, the EV-mediated maintenance of homeostasis and the regulation of physiological functions have remained less explored. Here, we provide a comprehensive overview of the current understanding of the physiological roles of EVs, which has been written by crowd-sourcing, drawing on the unique EV expertise of academia-based scientists, clinicians and industry based in 27 European countries, the United States and Australia. This review is intended to be of relevance to both researchers already working on EV biology and to newcomers who will encounter this universal cell biological system. Therefore, here we address the molecular contents and functions of EVs in various tissues and body fluids from cell systems to organs. We also review the physiological mechanisms of EVs in bacteria, lower eukaryotes and plants to highlight the functional uniformity of this emerging communication system.

Structures to complement the archaeo-eukaryotic primases catalytic cycle description: What's next?

DNA replication is a crucial stage in the transfer of genetic information from parent to daughter cells. This mechanism involves multiple proteins with one key player being the primase. Primases are single-stranded DNA dependent RNA polymerases. On the leading strand, they synthesize the primer once allowing DNA elongation while on the lagging strand primers are generated repeatedly (Okazaki fragments). Primases have the unique ability to create the first phosphodiester bond yielding a dinucleotide which is initially elongated by primases and then by DNA polymerases.

Primase activity has been studied in the last decades but the detailed molecular steps explaining some unique features remain unclear. High-resolution structures of free and bound primases domains have brought significant insights in the understanding of the primase reaction cycle. Here, we give a short review of the structural work conducted in the field of archaeo-eukaryotic primases and we underline the missing “pictures” of the active forms of the enzyme which are of major interest. We organized our analysis with respect to the progression through the catalytic pathway.

Identification of the minimal replicon and the origin of replication of the crenarchaeal plasmid pRN1

We have determined the minimal replicon of the crenarchaeal plasmid pRN1. It consists of 3097 base pairs amounting to 58% of the genome of pRN1. The minimal replicon comprises replication operon orf56/orf904 coding for a transcriptional repressor and the replication protein of pRN1. An upstream region of 64 bp that contains the promoter of the replication operon is essential as well as 166 bp of sequence downstream of the orf904 gene. This region contains a putative transcriptional terminator and a 100 nucleotides long stem–loop structure. Only the latter structure was shown to be required for replication. In addition replication was sustained when the stem–loop was displaced to another part of the pRN1 sequence. By mutational analysis we also find that the integrity of the stem–loop structure is required to maintain the replication of pRN1-derived constructs. As similar stem–loop structures are also present in other members of the pRN family, we suggest that this conserved structural element could be the origin of replication for the pRN plasmids. Further bioinformatic analysis revealed that the domain structure of the replication protein and the presence of a similar stem–loop structure as the putative replication origin are also found in several bacteriophages.

Patterns of depressive symptoms among patients with HIV infection

OBJECTIVE

To identify the level of depressive symptoms among patients with HIV infection and to examine the reported patterns of depressive symptoms not confounded by the physical manifestations of HIV-infection.

METHOD

A total of 191 patients with HIV infection (75 males (39%) and 116 females (61%), mean age 40.48 +/- 10 years), from three HIV clinics were administered the Beck Depression Inventory-II as well as a demographic questionnaire as part of a larger study.

RESULTS

Moderate to severe depressive symptoms were reported by 17.3% of the HIV-infected patients with females reporting significantly higher levels of depressive symptoms than males. A principal components analysis identified three clusters of depressive symptoms: cognitive-affective, negative cognitions and somatic symptoms. The HIV-infected patients were found to display mainly cognitive-affective symptoms of depression.

CONCLUSION

HIV-infected patients, especially female patients, may be at an increased risk of experiencing high levels of depressive symptoms. It is recommended that HIV-infected patients be routinely screened for depression, particularly cognitive-affective symptoms of depression.

The archaeo-eukaryotic primase of plasmid pRN1 requires a helix bundle domain for faithful primer synthesis

The plasmid pRN1 encodes for a multifunctional replication protein with primase, DNA polymerase and helicase activity. The minimal region required for primase activity encompasses amino-acid residues 40–370. While the N-terminal part of that minimal region (residues 47–247) folds into the prim/pol domain and bears the active site, the structure and function of the C-terminal part (residues 248–370) is unknown. Here we show that the C-terminal part of the minimal region folds into a compact domain with six helices and is stabilized by a disulfide bond. Three helices superimpose well with the C-terminal domain of the primase of the bacterial broad host range plasmid RSF1010. Structure-based site-directed mutagenesis shows that the C-terminal helix of the helix bundle domain is required for primase activity although it is distant to the active site in the crystallized conformation. Furthermore, we identified mutants of the C-terminal domain, which are defective in template binding, dinucleotide formation and conformation change prior to DNA extension.

Biofunctionalization of dispense-plotted hydroxyapatite scaffolds with peptides: quantification and cellular response

Hydroxyapatite (HA) ceramic is a widely used synthetic bone substitute material for the regeneration of bone defects. We manufactured HA scaffolds with adjustable pore sizes and pore geometry by dispense-plotting. In addition, we attached peptides covalently onto the HA surface and are able to simultaneously quantify the amount of covalently attached and adsorbed peptide down to the picomolar range with a novel fluorescence-based detection method. In cell culture assays with stromal bone marrow cells, we observed a positive effect of biofunctionalization on cell differentiation after 21 days of culture when comparing the scaffold functionalized with the RGD motif containing adhesion peptide to an unmodified scaffold.

Inducible and constitutive promoters for genetic systems in Sulfolobus acidocaldarius

Central to genetic work in any organism are the availability of a range of inducible and constitutive promoters. In this work we studied several promoters for use in the hyperthermophilic archaeon Sulfolobus acidocaldarius. The promoters were tested with the aid of an E. coli-Sulfolobus shuttle vector in reporter gene experiments. As the most suitable inducible promoter a maltose inducible promoter was identified. It comprises 266 bp of the sequence upstream of the gene coding for the maltose/maltotriose binding protein (mbp, Saci_1165). Induction is feasible with either maltose or dextrin at concentrations of 0.2-0.4%. The highest increase in expression (up to 17-fold) was observed in late exponential and stationary phase around 30-50 h after addition of dextrin. Whereas in the presence of glucose and xylose higher basal activity and reduced inducibility with maltose is observed, sucrose can be used in the growth medium additionally without affecting the basal activity or the inducibility. The minimal promoter region necessary could be narrowed down to 169 bp of the upstream sequence. The ABCE1 protein from S. solfataricus was successfully expressed under control of the inducible promoter with the shuttle vector pC and purified from the S. acidocaldarius culture with a yield of about 1 mg L(-1) culture. In addition we also determined the promoter strength of several constitutive promoters.

Structure-based stability analysis of an extremely stable dimeric DNA binding protein from Sulfolobus islandicus

ORF56 is a small and thermodynamically extremely stable dimeric protein from the archaeon Sulfolobus islandicus. This DNA binding protein is encoded on plasmid pRN1 and possibly controls the copy number of the plasmid. We report the solution NMR structure as well as the crystal structure of ORF56 comprising a ribbon-helix-helix fold. The homodimer consists of an antiparallel intersubunit beta-sheet and two alpha-helices per monomer, which is a common DNA binding fold of plasmid- and phage-encoded gene regulation proteins. NMR titration experiments with ORF56 and double-stranded DNA derived from its promoter binding site revealed that it is largely the beta-sheets that interact with the DNA. The beta-sheet experiences high local fluctuations, which are conserved among DNA binding ribbon-helix-helix dimers from mesophilic and hyperthermophilic organisms. In contrast, residues strongly protected against H-D exchange are localized in helix 2, forming the hydrophobic intermolecular core of the dimer. A structure-based comparison of the intermolecular binding surface and the change in accessible surface area upon unfolding of various ribbon-helix-helix dimers with the Gibbs free energy changes and m values show a correlation between hydrophobicity of these surface areas and stability. These findings provide possible explanations for the very high thermodynamic stability of ORF56 with retained DNA binding capacity.

DNA translocation activity of the multifunctional replication protein ORF904 from the archaeal plasmid pRN1

The replication protein ORF904 from the plasmid pRN1 is a multifunctional enzyme with ATPase-, primase- and DNA polymerase activity. Sequence analysis suggests the presence of at least two conserved domains: an N-terminal prim/pol domain with primase and DNA polymerase activities and a C-terminal superfamily 3 helicase domain with a strong double-stranded DNA dependant ATPase activity. The exact molecular function of the helicase domain in the process of plasmid replication remains unclear. Potentially this motor protein is involved in duplex remodelling and/or origin opening at the plasmid replication origin. In support of this we found that the monomeric replication protein ORF904 forms a hexameric ring in the presence of DNA. It is able to translocate along single-stranded DNA in 3′–5′ direction as well as on double-stranded DNA. Critical residues important for ATPase activity and DNA translocation activity were identified and are in agreement with a homology model of the helicase domain. In addition we propose that a winged helix DNA-binding domain at the C-terminus of the helicase domain could assist the binding of the replication protein specifically to the replication origin.

Molecular modeling and functional characterization of the monomeric primase-polymerase domain from the Sulfolobus solfataricus plasmid pIT3

A tri-functional monomeric primase-polymerase domain encoded by the plasmid pIT3 from Sulfolobus solfataricus strain IT3 was identified using a structural-functional approach. The N-terminal domain of the pIT3 replication protein encompassing residues 31-245 (i.e. Rep245) was modeled onto the crystallographic structure of the bifunctional primase-polymerase domain of the archaeal plasmid pRN1 and refined by molecular dynamics in solution. The Rep245 protein was purified following overexpression in Escherichia coli and its nucleic acid synthesis activity was characterized. The biochemical properties of the polymerase activity such as pH, temperature optima and divalent cation metal dependence were described. Rep245 was capable of utilizing both ribonucleotides and deoxyribonucleotides for de novo primer synthesis and it synthesized DNA products up to several kb in length in a template-dependent manner. Interestingly, the Rep245 primase-polymerase domain harbors also a terminal nucleotidyl transferase activity, being able to elongate the 3'-end of synthetic oligonucleotides in a non-templated manner. Comparative sequence-structural analysis of the modeled Rep245 domain with other archaeal primase-polymerases revealed some distinctive features that could account for the multifaceted activities exhibited by this domain. To the best of our knowledge, Rep245 typifies the shortest functional domain from a crenarchaeal plasmid endowed with DNA and RNA synthesis and terminal transferase activity.

Genetic tools for Sulfolobus spp.: vectors and first applications

Sulfolobus species belong to the best-studied archaeal organisms but have lacked powerful genetic methods. Recently, there has been considerable progress in the field of Sulfolobus genetics. Urgently needed basic genetic tools, such as targeted gene knockout techniques and shuttle vectors are being developed at an increasing pace. For S. solfataricus knockout systems as well as different shuttle vectors are available. For the genetically more stable S. acidocaldarius shuttle vectors have been recently developed. In this review we summarize the currently available genetic tools and methods for the genus Sulfolobus. Different transformation protocols are discussed, as well as all so far developed knockout systems and Sulfolobus-Escherichia coli shuttle vectors are summarized. Special emphasis is put on the important vector components, i.e., selectable markers and Sulfolobus replicons. Additionally, the information gathered on different Sulfolobus strains with respect to their use as recipient strains is reviewed. The advantages and disadvantages of the different systems are discussed and aims for further improvement of genetic systems are identified.

Component structure of the SF-36 in Jamaicans with sickle cell disease

OBJECTIVES

Sickle cell disease (SCD) is the commonest genetic disorder in Jamaica and greatly affects the quality of life (QOL) of those who are afflicted. The Short Form 36 survey (SF-36) questionnaire is one of the most commonly utilized measures of QOL. Physicians cannot interpret QOL measures until the instruments being used to make assessment are adequately established in their population. The Jamaican cultural and educational systems expose its people to many stresses which likely impact on their QOL. It is thus postulated that the QOL construct may exhibit a different structure for the population with sickle cell disease.

SUBJECTS AND METHODS

The SF-36 v.2 was interviewer administered to the Jamaican Sickle Cell Disease Cohort Study participants ('Cohort' sample) and a random sample of adult sickle cell unit patients ('Main'sample). Demographic data were also collected on both groups. Both of the samples did not meet the five rule criteria for compliance with the original SF-36 component structure. Hence, principal components analysis was used to determine the component structure of the SF-36 in both groups.

RESULTS

Three dimensions may underlie the SF-36 for both groups and these could be labelled 'Physical Health', 'Mental Health' and 'Role Limitations'. This solution accounted for 45.8% of the variability underlying the SF-36 in the 'Cohort'sample and 54.6% of the variability in the 'Main' sample.

CONCLUSIONS

It concluded that within Jamaican samples of patients with sickle cell disease, the SF-36 has a component structure which is quite distinct from that initially proposed by its creators.

Properties of an unusual DNA primase from an archaeal plasmid

Primases are specialized DNA-dependent RNA polymerases that synthesize a short oligoribonucleotide complementary to single-stranded template DNA. In the context of cellular DNA replication, primases are indispensable since DNA polymerases are not able to start DNA polymerization de novo.

The primase activity of the replication protein from the archaeal plasmid pRN1 synthesizes a rather unusual mixed primer consisting of a single ribonucleotide at the 5′ end followed by seven deoxynucleotides. Ribonucleotides and deoxynucleotides are strictly required at the respective positions within the primer. Furthermore, in contrast to other archaeo-eukaryotic primases, the primase activity is highly sequence-specific and requires the trinucleotide motif GTG in the template. Primer synthesis starts outside of the recognition motif, immediately 5′ to the recognition motif. The fidelity of the primase synthesis is high, as non-complementary bases are not incorporated into the primer.

Small multicopy, non-integrative shuttle vectors based on the plasmid pRN1 for Sulfolobus acidocaldarius and Sulfolobus solfataricus, model organisms of the (cren-)archaea

The extreme thermoacidophiles of the genus Sulfolobus are among the best-studied archaea but have lacked small, reliable plasmid vectors, which have proven extremely useful for manipulating and analyzing genes in other microorganisms. Here we report the successful construction of a series of Sulfolobus-Escherichia coli shuttle vectors based on the small multicopy plasmid pRN1 from Sulfolobus islandicus. Selection in suitable uracil auxotrophs is provided through inclusion of pyrEF genes in the plasmid. The shuttle vectors do not integrate into the genome and do not rearrange. The plasmids allow functional overexpression of genes, as could be demonstrated for the beta-glycosidase (lacS) gene of S. solfataricus. In addition, we demonstrate that this beta-glycosidase gene could function as selectable marker in S. solfataricus. The shuttle plasmids differ in their interruption sites within pRN1 and allowed us to delineate functionally important regions of pRN1. The orf56/orf904 operon appears to be essential for pRN1 replication, in contrast interruption of the highly conserved orf80/plrA gene is tolerated. The new vector system promises to facilitate genetic studies of Sulfolobus and to have biotechnological uses, such as the overexpression or optimization of thermophilic enzymes that are not readily performed in mesophilic hosts.

An active nonautonomous mobile element in Sulfolobus islandicus REN1H1

In the crenarchaeote Sulfolobus islandicus REN1H1, a mobile element of 321 bp length has been shown to be active. It does not contain terminal inverted repeats and transposes by a replicative mechanism. This newly discovered element has been named SMN1 (for Sulfolobus miniature noninverted repeat transposable element).

Characterization of the transcriptional activity of the cryptic plasmid pRN1 from Sulfolobus islandicus REN1H1 and regulation of its replication operon

The plasmid pRN1 from Sulfolobus islandicus REN1H1 belongs to the crenarchaeal plasmid family pRN. The plasmids in this family encode three conserved proteins that participate in plasmid replication and copy number regulation, as suggested by biochemical characterization of the recombinant proteins. In order to deepen our understanding of the molecular biology of these plasmids, we investigated the transcriptional activity of the model plasmid pRN1. We detected five major transcripts present at about 2 to 15 copies per cell. One long transcriptional unit comprises the genes for the plasmid-copy-number control protein Orf56/CopG and the replication protein Orf904. A second transcript with a long 3'-untranslated region codes for the DNA binding protein Orf80. For both transcripts, we identified countertranscripts which could play a regulatory role. The function of the fifth transcript is unclear. For the five transcripts, we determined the start site, the transcript end, the stability, and the abundance in different growth phases. Reporter gene experiments demonstrated that the copy number control protein Orf56 represses transcription of the orf56-orf904 cotranscript in vivo.

Characterisation of the novel restriction endonuclease SuiI from Sulfolobus islandicus

A restriction endonuclease activity from Sulfolobus islandicus REN2H1 was purified by phosphocellulose and cation exchange chromatography. The enzyme cuts DNA at the recognition site GCwGC as could be shown by restriction analysis of plasmids and short synthetic duplex DNA. The cleavage occurs after the first guanosine base and is inhibited by 5-methyl-cytosine methylation. The restriction activity is salt-sensitive and has an optimal activity around 70 degrees C.

Plasmids and viruses of the thermoacidophilic crenarchaeote Sulfolobus

The crenarchaeote Sulfolobus spp. is a host for a remarkably large spectrum of viruses and plasmids. The genetic elements characterized so far indicate a large degree of novelty in terms of morphology (viruses) and in terms of genome content (plasmids and viruses). The viruses and conjugative plasmids encode a great number of conserved proteins of unknown function due to the lack of sequence similarity to functionally characterized proteins. These apparently essential proteins remain to be studied and should help to understand the physiology and genetics of the respective genetic elements as well as the host. Sulfolobus is one of the best-studied archaeons and could develop into an important model organism of the crenarchaea and the archaea.

Thermodynamic Analysis of the Single-Stranded DNA Binding Activity of the Archaeal Replication Protein A (RPA) from Sulfolobus solfataricus

The single-stranded DNA binding protein from Sulfolobus solfataricus (Sso-RPA) binds single-stranded DNA with dissociation constants in the range of 10-30 nM at room temperature. The affinity for DNA decreases at higher temperatures. At 85 degrees C, the optimal growth temperature of the crenarchaeot S. solfataricus, the dissociation constant is only about 1 microM. We analyzed the equilibrium between Sso-RPA and a fluorescently labeled 13 nucleotide oligonucleotide by fluorescence anisotropy measurements in the presence of four different salts and in the temperature range between 10 and 60 degrees C. In the presence of potassium chloride and choline chloride, three to four ions are released upon complexation, independent of the temperature. In contrast, in the presence of potassium fluoride and potassium glutamate, we observed a significant change of the number of ions released when the temperature was varied. The binding reaction is strongly exothermic with enthalpies of about -55 to -70 kJ/mol, depending upon the salt. Van't Hoff analysis suggests that the binding enthalpy is temperature independent.

In vitro selection of DNA binding sites for ABF1 protein from Saccharomyces cerevisiae

The autonomously replicating sequence-binding factor 1 (ABF1) from Sacchramoyces cerevisiae is known as a multifunctional DNA binding protein that is involved in transcriptional regulation, DNA-replication, and in restructuring of chromatin via nucleosome remodelling. ABF1 binds to DNA sequences found in ARS elements and in various transcriptional regulatory elements. This led to the early definition of the consensus motive 5'-CGTnnnnnnnGA(G/C)-3'. We have used a SELEX approach to expand and better characterize the DNA sequence requirements of ABF1. Starting from a pool of oligonucleotides randomized at a sequence of 30 nucleotides, we used EMSA to select for sequences with high affinity for ABF1. We obtained the sequences of 106 aptamers after the 15th SELEX round. A 16 nucleotide consensus was derived from this pool by analysis with the motif search programme MEME. Quantitative EMSA experiments verified our experimental approach since binding sequences which were bound with high affinity occurred more often in the pool and resembled the derived consensus to a higher degree. We found DNA sequences that are bound by ABF1 with nearly two-magnitude higher affinity as compared to the hitherto accepted ABF1 consensus sequence. This led us to postulate a strong recognition motive: 5'-TnnCGTnnnnnnTGAT-3'.

A highly acid-stable and thermostable endo-beta-glucanase from the thermoacidophilic archaeon Sulfolobus solfataricus

The thermoacidophilic archaeon Sulfolobus solfataricus P2 encodes three hypothetic endo-beta-glucanases, SSO1354, SSO1949 and SSO2534. We cloned and expressed the gene sso1949 encoding the 334 amino acids containing protein SSO1949, which can be classified as a member of glycoside hydrolase family 12. The purified recombinant enzyme hydrolyses carboxymethylcellulose as well as cello-oligomers, with cellobiose and cellotriose as main reaction products. By following the hydrolysis of a fluorescently labelled cellohexaoside under a wide variety of conditions, we show that SSO1949 is a unique extremophilic enzyme. This archaeal enzyme has a pH optimum of approx. pH 1.8 and a temperature optimum of approx. 80 degrees C. Furthermore, the enzyme is thermostable, with a half-life of approx. 8 h at 80 degrees C and pH 1.8. The thermostability is strongly pH-dependent. At neutral pH, the thermal inactivation rate is nearly two orders of magnitude higher than at pH 1.8. Homology modelling suggests that the catalytic domain of SSO1949 has a similar fold to other mesophilic, acidophilic and neutral cellulases. The presence of a signal peptide indicates that SSO1949 is a secreted protein, which enables S. solfataricus to use cellulose as an external carbon source. It appears that SSO1949 is perfectly adapted to the extreme environment in solfataric pools. A cellulolytic enzyme with such a combination of stability and activity at high temperatures and low pH has not been described so far and could be a valuable tool for the large-scale hydrolysis of cellulose under acidic conditions.

Site-Specific Binding of the 9.5 Kilodalton DNA-Binding Protein ORF80 Visualized by Atomic Force Microscopy

Atomic force microscopy (AFM) has been used to examine the binding properties of the DNA-binding protein ORF80 to DNA. ORF80 is a 9.5 kDa protein that binds site-specifically to double-stranded DNA of the sequence TTAA-N(7)-TTAA. Direct sizing of the protein complexes on DNA fragments from the plasmid pRN1 with AFM shows that the protein ORF80 binds preferentially to two positions. These positions agree well with the ORF80 binding sites determined by footprinting analysis. The measurements allow an estimate of the stoichiometry of the DNA-protein complexes. In contrast to previous results, the single-molecule experiments suggest that only a low number of ORF80 molecules bind to a DNA-binding site.

The replication protein of the Sulfolobus islandicus plasmid pRN1

The thermoacidophile crenarchaeote Sulfolobus ssp. is one of the best-studied Archaea. Cryptic and conjugative plasmids as well as viruses have been described for this genus. For the majority of the genetic elements only the genome sequence and the basic characteristics were determined. In contrast the fusellovirus SSV1 and the cryptic plasmid pRN1, which is the smallest known genetic element of the crenarchaeota, have been studied in more detail. The three gene products of the plasmid pRN1 have been characterized biochemically. The replication protein of the plasmid, a multifunctional enzyme, has a novel domain, termed prim/pol domain. This domain constitutes the first member of the DNA polymerase family E. Based on the biochemical characterization of the gene products a model of how pRN1 is replicated in vivo is proposed.

Folding and association of an extremely stable dimeric protein from Sulfolobus islandicus

ORF56 is a plasmid-encoded protein from Sulfolobus islandicus, which probably controls the copy number of the pRN1 plasmid by binding to its own promotor. The protein showed an extremely high stability in denaturant, heat, and pH-induced unfolding transitions, which can be well described by a two-state reaction between native dimers and unfolded monomers. The homodimeric character of native ORF56 was confirmed by analytical ultracentrifugation. Far-UV circular dichroism and fluorescence spectroscopy gave superimposable denaturant-induced unfolding transitions and the midpoints of both heat as well as denaturant-induced unfolding depend on the protein concentration supporting the two-state model. This model was confirmed by GdmSCN-induced unfolding monitored by heteronuclear 2D NMR spectroscopy. Chemical denaturation was accomplished by GdmCl and GdmSCN, revealing a Gibbs free energy of stabilization of -85.1 kJ/mol at 25 degrees C. Thermal unfolding was possible only above 1 M GdmCl, which shifted the melting temperature (t(m)) below the boiling point of water. Linear extrapolation of t(m) to 0 M GdmCl yielded a t(m) of 107.5 degrees C (5 microM monomer concentration). Additionally, ORF56 remains natively structured over a remarkable pH range from pH 2 to pH 12. Folding kinetics were followed by far-UV CD and fluorescence after either stopped-flow or manual mixing. All kinetic traces showed only a single phase and the two probes revealed coincident folding rates (k(f), k(u)), indicating the absence of intermediates. Apparent first-order refolding rates depend linearly on the protein concentration, whereas the unfolding rates do not. Both lnk(f) and lnk(u) depend linearly on the GdmCl concentration. Together, folding and association of homodimeric ORF56 are concurrent events. In the absence of denaturant ORF56 refolds fast (7.0 x 10(7)M(-1)s(-1)) and unfolds extremely slowly (5.7 year(-1)). Therefore, high stability is coupled to a slow unfolding rate, which is often observed for proteins of extremophilic organisms.

Structure of a bifunctional DNA primase-polymerase

Genome replication generally requires primases, which synthesize an initial oligonucleotide primer, and DNA polymerases, which elongate the primer. Primase and DNA polymerase activities are combined, however, in newly identified replicases from archaeal plasmids, such as pRN1 from Sulfolobus islandicus. Here we present a structure-function analysis of the pRN1 primase-polymerase (prim-pol) domain. The crystal structure shows a central depression lined by conserved residues. Mutations on one side of the depression reduce DNA affinity. On the opposite side of the depression cluster three acidic residues and a histidine, which are required for primase and DNA polymerase activity. One acidic residue binds a manganese ion, suggestive of a metal-dependent catalytic mechanism. The structure does not show any similarity to DNA polymerases, but is distantly related to archaeal and eukaryotic primases, with corresponding active-site residues. We propose that archaeal and eukaryotic primases and the prim-pol domain have a common evolutionary ancestor, a bifunctional replicase for small DNA genomes.

A novel type of replicative enzyme harbouring ATPase, primase and DNA polymerase activity

Although DNA replication is a process common in all domains of life, primase and replicative DNA polymerase appear to have evolved independently in the bacterial domain versus the archaeal/eukaryal branch of life. Here, we report on a new type of replication protein that constitutes the first member of the DNA polymerase family E. The protein ORF904, encoded by the plasmid pRN1 from the thermoacidophile archaeon Sulfolobus islandicus, is a highly compact multifunctional enzyme with ATPase, primase and DNA polymerase activity. Recombinant purified ORF904 hydrolyses ATP in a DNA-dependent manner. Deoxynucleotides are preferentially used for the synthesis of primers approximately 8 nucleotides long. The DNA polymerase activity of ORF904 synthesizes replication products of up to several thousand nucleotides in length. The primase and DNA polymerase activity are located in the N-terminal half of the protein, which does not show homology to any known DNA polymerase or primase. ORF904 constitutes a new type of replication enzyme, which could have evolved independently from the eubacterial and archaeal/eukaryal proteins of DNA replication.

The XPC-HR23B complex displays high affinity and specificity for damaged DNA in a true-equilibrium fluorescence assay

The XPC-HR23B complex is a prime candidate for the initial damage recognition step during global genome nucleotide excision repair. A specific interaction between the XPC-HR23B complex and various types of damaged DNA substrates has been demonstrated in recent work by electrophoretic mobility shift assays or immunoprecipitation. Although these studies allowed the estimation of relative binding affinities for the different types of lesions, the presence of large amounts of competitor DNA or the need for glutaraldehyde fixation prevented the quantification of equilibrium constants. We have performed a quantitative study on the binding of XPC to damaged DNA using fluorescence anisotropy measurements. The XPC-HR23B complex binds with high affinity (K(D) approximately 1-3 nM) to fluorescent 36 bp DNA fragments containing a single cisplatin 1,3-intrastrand adduct or a six-nucleotide mispaired region. From stoichiometric titration experiments, it is concluded that approximately 70% of the XPC-HR23B preparation is active in DNA binding. Binding experiments employing fluorescent probes with a single defined photoproduct reveal a 30-fold preference of XPC for 6,4-photoproducts as compared to a cyclobutane dimer. Competition experiments with undamaged and damaged plasmid DNA indicate that the XPC-HR23B complex discriminates between damaged and undamaged sites with high specificity. The specificity factor is between 100 and 3000, depending on the number of nonspecific sites considered in the calculations. Upon addition of XPA to the XPC binding reaction mixtures, it was not possible to detect cooperative ternary complex formation on the platinated 36 bp probe.

The protein ORF80 from the acidophilic and thermophilic archaeon Sulfolobus islandicus binds highly site-specifically to double-stranded DNA and represents a novel type of basic leucine zipper protein

The cryptic high copy number plasmid pRN1 from the thermophilic and acidophilic crenarchaeote Sulfolobus islandicus shares three conserved open reading frames with other S.islandicus plasmids. One of the open reading frames, namely orf80, encodes a 9.5 kDa protein that has no homology to any characterised protein. Recombinant ORF80 purified from Escherichia coli binds to double-stranded DNA in a sequence-specific manner as suggested by EMSA experiments and DNase I footprints. Two highly symmetrical binding sites separated by approximately 60 bp were found upstream of the orf80 gene. Both binding sites contain two TTAA motifs as well as other conserved bases. Fluorescence measurements show that short duplex DNAs derived from a single binding site sequence are bound with submicromolar affinity and moderate cooperativity by ORF80. On DNA fragments carrying both binding sites, a rather large protein-DNA complex is formed in a highly cooperative manner. ORF80 contains an N-terminal leucine zipper motif and a highly basic domain at its C-terminus. Compared to all known basic leucine zipper proteins the order of the domains is reversed in ORF80. ORF80 may therefore constitute a new subclass of basic leucine zipper DNA-binding proteins.

Binding of XPA and RPA to damaged DNA investigated by fluorescence anisotropy

The proteins XPA and RPA are assumed to be involved in primary damage recognition of global genome nucleotide excision repair. XPA as well as RPA have been each reported to specifically bind DNA lesions, and ternary complex formation with damaged DNA has also been shown. We employed fluorescence anisotropy measurements to study the DNA-binding properties of XPA and RPA under true equilibrium conditions using damaged DNA probes carrying a terminal fluorescein modification as a reporter. XPA binds with low affinity and in a strongly salt-dependent manner to DNA containing a 1,3-d(GTG) intrastrand adduct of the anticancer drug cisplatin or a 6-nt mismatch (K(D) = 400 nM) with 3-fold preference for damaged vs undamaged DNA. At near physiological salt conditions binding is very weak (K(D) > 2 microM). RPA binds to damaged DNA probes with dissociation constants in the range of 20 nM and a nearly 15-fold preference over undamaged DNA. The presence of a cisplatin modification weakens the affinity of RPA for single-stranded DNA by more than 1 order of magnitude indicating that binding to the lesion itself is not a driving force in damage recognition. Our fluorescence anisotropy assays also show that the presence of XPA does not enhance the affinity of RPA for damaged DNA although both proteins interact. In contrast, cooperative binding of XPA and RPA is observed in EMSA. Our results point to a damage-sensing function of the XPA-RPA complex with RPA mediating the important DNA contacts.

Thermostable and site-specific DNA binding of the gene product ORF56 from the Sulfolobus islandicus plasmid pRN1, a putative archael plasmid copy control protein

There is still a lack of information on the specific characteristics of DNA-binding proteins from hyperthermophiles. Here we report on the product of the gene orf56 from plasmid pRN1 of the acidophilic and thermophilic archaeon Sulfolobus islandicus. orf56 has not been characterised yet but low sequence similarily to several eubacterial plasmid-encoded genes suggests that this 6.5 kDa protein is a sequence-specific DNA-binding protein. The DNA-binding properties of ORF56, expressed in Escherichia coli, have been investigated by EMSA experiments and by fluorescence anisotropy measurements. Recombinant ORF56 binds to double-stranded DNA, specifically to an inverted repeat located within the promoter of orf56. Binding to this site could down-regulate transcription of the orf56 gene and also of the overlapping orf904 gene, encoding the putative initiator protein of plasmid replication. By gel filtration and chemical crosslinking we have shown that ORF56 is a dimeric protein. Stoichiometric fluorescence anisotropy titrations further indicate that ORF56 binds as a tetramer to the inverted repeat of its target binding site. CD spectroscopy points to a significant increase in ordered secondary structure of ORF56 upon binding DNA. ORF56 binds without apparent cooperativity to its target DNA with a dissociation constant in the nanomolar range. Quantitative analysis of binding isotherms performed at various salt concentrations and at different temperatures indicates that approximately seven ions are released upon complex formation and that complex formation is accompanied by a change in heat capacity of -6.2 kJ/mol. Furthermore, recombinant ORF56 proved to be highly thermostable and is able to bind DNA up to 85 degrees C.

Adenylosuccinate synthase from Saccharomyces cerevisiae: homologous overexpression, purification and characterization of the recombinant protein

Adenylosuccinate synthase (EC 6.3.4.4) catalyses the first committed step in the synthesis of adenosine. We have overexpressed the cloned gene of Saccharomyces cerevisiae (ADE12) in S. cerevisiae. The recombinant enzyme exhibits similar kinetic behaviour to that of the native enzyme purified from S. cerevisiae. This ter-reactant dimeric enzyme shows Michaelis-Menten kinetics only with IMP. l-Aspartate and GTP display a weak negative co-operativity (Hill coefficient 0. 8-0.9). This negative co-operativity has not yet been reported for adenylosuccinate synthases from other organisms. Another unusual feature of the enzyme from S. cerevisiae is its negligible inhibition by adenine nucleotides and its pronounced inhibition by Cl(-) ions.

Photocrosslinking locates a binding site for the large subunit of human replication protein A to the damaged strand of cisplatin-modified DNA

The repair proteins XPA, XPC and replication protein A (RPA) have been implicated in the primary recognition of damaged DNA sites during nucleotide excision repair. Detailed structural information on the binding of these proteins to DNA lesions is however lacking. We have studied the binding of human RPA (hRPA) and hRPA-XPA-complexes to model oligonucleo-tides containing a single 1, 3-d(GTG)-cisplatin-modification by photocrosslinking and electrophoretic mobility shift experiments. The 70 kDa subunit of hRPA can be crosslinked with high efficiency to cisplatin-modified DNA probes carrying 5-iodo-2"-deoxyuridin (5-IdU) as crosslinking chromophore. High efficiency crosslinking is dependent on the presence of the DNA lesion and occurs preferentially at its 5"-side. Examination of the crosslinking efficiency in dependence on the position of the 5-IdU chromophore indicates a specific positioning of hRPA with respect to the platination site. When hRPA and XPA are both present mainly hRPA is crosslinked to the DNA. Our mobility shift experiments directly show the formation of a stable ternary complex of hRPA, XPA and the damaged DNA. The affinity of the XPA-hRPA complex to the damaged DNA is increased by more than one order of magnitude as compared to hRPA alone.

Identification of the binding site for the extrahelical target base in N6-adenine DNA methyltransferases by photo-cross-linking with duplex oligodeoxyribonucleotides containing 5-iodouracil at the target position

DNA methyltransferases flip their target bases out of the DNA double helix for catalysis. Base flipping of C5-cytosine DNA methyltransferases was directly observed in the protein-DNA cocrystal structures of M.HhaI and M.HaeIII. Indirect structural evidence for base flipping of N6-adenine and N4-cytosine DNA methyltransferases was obtained by modeling DNA into the three-dimensional structures of M.TaqI and M.PvuII in complex with the cofactor. In addition, biochemical evidence of base flipping was reported for different N6-adenine DNA methyltransferases. As no protein-DNA cocrystal structure for the related N6-adenine and N4-cytosine DNA methyltransferases is available, we used light-induced photochemical cross-linking to identify the binding site of the extrahelical target bases. The N6-adenine DNA methyltransferases M.TaqI and M.CviBIII, which both methylate adenine within the double-stranded 5'-TCGA-3' DNA sequence, were photo-cross-linked to duplex oligodeoxyribonucleotides containing 5-iodouracil at the target position in 50-60% and almost quantitative yield, respectively. Proteolytic fragmentation of the M. CviBIII-DNA complex followed by Edman degradation and electrospray ionization mass spectrometry indicates photo-cross-linking to tyrosine 122. In addition, the mutant methyltransferases M. TaqI/Y108A and M.TaqI/F196A were photo-cross-linked with 6-fold and 2-fold reduced efficiency, respectively, which suggests that tyrosine 108 is the primary site of modification in M.TaqI. Our results indicate a close proximity between the extrahelical target base and tyrosine 122 in M.CviBIII or tyrosine 108 in M.TaqI. As both residues belong to the conserved motif IV ((N/D/S)(P/I)P(Y/F/W)) found in all N6-adenine and N4-cytosine DNA as well as in N6-adenine RNA methyltransferases, a similar spatial relationship between the target bases and the aromatic amino acid residue within motif IV is expected for all these methyltransferases.

Cathepsin B of Schistosoma mansoni. Purification and activation of the recombinant proenzyme secreted by Saccharomyces cerevisiae

Procathepsin B from the parasitic trematode Schistosoma mansoni was expressed as a glycosylation-minus mutant in yeast cells and purified by means of a histidine affinity tag which was added to the carboxyl terminus of the recombinant protein. The purified zymogen underwent autoprocessing but required an assisting protease for activation. Pepsin-activated schistosomal cathepsin B was further characterized with the cathepsin B-specific substrates N-benzyloxycarbonyl (Z)-Arg-Arg-p-nitroanilide, Z-Arg-Arg-7-amido-4-methyl-coumarin, and Z-Phe-Arg-7-amido-4-methylcoumarin. A proteolytic activity comparable to mammalian cathepsin B was observed. In addition, we analyzed the degradation of human hemoglobin by schistosomal cathepsin B, which has been suggested to be the physiological target of the protease.

The impact of an interinstitutional relocation on nursing home residents requiring a high level of care

Residents of two older nursing homes (n = 196) were relocated to a new 238-bed facility. A nonequivalent control group (n = 74) design with two pretests and two posttests was used to assess the impact of this move on their well-being and health. The relocated residents and control-group residents required a similar level of nursing care. Residents to be relocated participated in a preparation program designed to enhance their sense of control and predictability over the move. Analyses of medical records, nurses' ratings, and interviews strongly suggest that the move had no negative effect on the residents as a group or on vulnerable subgroups of residents.