IgA plasma cells in vascular tissue of patients with Kawasaki syndrome

The etiology and pathogenesis of Kawasaki syndrome (KS) remain unknown. Clinical and epidemiologic features of KS are consistent with an infectious cause. To search for an etiologic agent of KS, a phage cDNA expression library was constructed from the aorto-iliac junction of a patient with fatal acute KS and screened with convalescent KS serum followed by anti-human Ig. Unexpectedly, 0.1% of the clones in the library react with anti-human Ig, indicating the presence of many Ig-producing B lymphocytes in the vasculitic tissue. To confirm this finding and to determine the isotypes produced, frozen vascular tissue sections from the patient and paraffin sections from coronary arteries from six additional patients with fatal acute or subacute KS were incubated with Abs to Ig isotypes. Histopathology of the tissues revealed the presence of many plasma cells in the inflammatory infiltrate. IgA was the predominant isotype produced in vascular tissue in all seven KS patients. IgM- and IgG-producing cells were less often detected. We conclude that there is a marked plasma cell response within the vasculitic tissue in KS, with unusual IgA production locally in this nonlymphoid, nonmucosal tissue. We suggest that the prominence of IgA plasma cells in the vascular infiltrate in the early, acute, and subacute stages of KS indicates an Ag-driven immune response to an etiologic agent with a respiratory or gastrointestinal portal of entry and speculate that this unusual immune response is integral to the pathogenesis of the illness.

IgA plasma cells in vascular tissue of patients with Kawasaki syndrome

The etiology and pathogenesis of Kawasaki syndrome (KS) remain unknown. Clinical and epidemiologic features of KS are consistent with an infectious cause. To search for an etiologic agent of KS, a phage cDNA expression library was constructed from the aorto-iliac junction of a patient with fatal acute KS and screened with convalescent KS serum followed by anti-human Ig. Unexpectedly, 0.1% of the clones in the library react with anti-human Ig, indicating the presence of many Ig-producing B lymphocytes in the vasculitic tissue. To confirm this finding and to determine the isotypes produced, frozen vascular tissue sections from the patient and paraffin sections from coronary arteries from six additional patients with fatal acute or subacute KS were incubated with Abs to Ig isotypes. Histopathology of the tissues revealed the presence of many plasma cells in the inflammatory infiltrate. IgA was the predominant isotype produced in vascular tissue in all seven KS patients. IgM- and IgG-producing cells were less often detected. We conclude that there is a marked plasma cell response within the vasculitic tissue in KS, with unusual IgA production locally in this nonlymphoid, nonmucosal tissue. We suggest that the prominence of IgA plasma cells in the vascular infiltrate in the early, acute, and subacute stages of KS indicates an Ag-driven immune response to an etiologic agent with a respiratory or gastrointestinal portal of entry and speculate that this unusual immune response is integral to the pathogenesis of the illness.

Generation of coronavirus spike deletion variants by high-frequency recombination at regions of predicted RNA secondary structure

Coronavirus RNA evolves in the central nervous systems (CNS) of mice during persistent infection. This evolution can be monitored by detection of a viral quasispecies of spike deletion variants (SDVs) (C. L. Rowe, S. C. Baker, M. J. Nathan, and J. O. Fleming, J. Virol. 71:2959-2969, 1997). We and others have found that the deletions cluster in the region from 1,200 to 1,800 nucleotides from the 5' end of the spike gene sequence, termed the "hypervariable" region. To address how SDVs might arise, we generated the predicted folding structures of the positive- and negative-strand senses of the entire 4,139-nt spike RNA sequence. We found that a prominent, isolated stem-loop structure is coincident with the hypervariable region in each structure. To determine if this predicted stem-loop is a "hot spot" for RNA recombination, we assessed whether this region of the spike is more frequently deleted than three other selected regions of the spike sequence in a population of viral sequences isolated from the CNS of acutely and persistently infected mice. Using differential colony hybridization of cloned spike reverse transcription-PCR products, we detected SDVs in which the hot spot was deleted but did not detect SDVs in which other regions of the spike sequence were exclusively deleted. Furthermore, sequence analysis and mapping of the crossover sites of 25 distinct patterns of SDVs showed that the majority of crossover sites clustered to two regions at the base of the isolated stem-loop, which we designated as high-frequency recombination sites 1 and 2. Interestingly, the majority of the left and right crossover sites of the SDVs were directly across from or proximal to one another, suggesting that these SDVs are likely generated by intramolecular recombination. Overall, our results are consistent with there being an important role for the spike RNA secondary structure as a contributing factor in the generation of SDVs during persistent infection.

Prefrontal dysfunction in depressed patients performing a complex planning task: a study using positron emission tomography

INTRODUCTION

Patients with unipolar depression show impaired performance on the Tower of London planning task. Positron emission tomography, which has previously identified resting state blood flow abnormalities in depression, was used to investigate neural activity associated with performance of this task in depressed patients and normal controls.

METHODS

Six patients with unipolar depression and six matched controls were scanned while performing easy and hard Tower of London problems in a one-touch computerized paradigm and while performing a perceptuomotor control task.

RESULTS

The patients in this study showed an expected task-related performance deficit compared with normal subjects. In normal subjects, the task engaged a network of prefrontal cortex, anterior cingulate, posterior cortical areas and subcortical structures including the striatum, thalamus and cerebellum. Depressed patients failed to show significant activation in the cingulate and striatum; activation in the other prefrontal and posterior cortical regions was significantly attenuated relative to controls. Crucially, patients also failed to show the normal augmentation of activation in the caudate nucleus, anterior cingulate and right prefrontal cortex associated with increasing task difficulty.

CONCLUSIONS

These findings provide evidence for cingulate, prefrontal and striatal dysfunction associated with impaired task performance in depression. The present results are consistent with a central role of cingulate dysfunction in depression as well as suggesting impaired frontostriatal function.

Cytochrome cd1 structure: unusual haem environments in a nitrite reductase and analysis of factors contributing to beta-propeller folds

The central tunnel of the eight-bladed beta-propeller domain of cytochrome cd1 (nitrite reductase) is seen, from a 1.28 A resolution structure, to contain hydrogen donors and acceptors that are satisfied by interaction either with water or the d1 haem. The d1 haem, although bound by an extensive network of hydrogen bonds, is not distorted in its binding pocket and is confirmed to have exactly the dioxoisobacteriochlorin structure proposed from chemical studies. A biological rationale is advanced for the undistorted structure of the d1 haem and the large number of hydrogen bonds it makes. The beta-propeller domain can be closely superimposed on that of methanol dehydrogenase despite the enzymes sharing no common sequence motifs and using a different set of interactions to "Velcro" close the propeller. The sequence and likely structural relationships between cytochrome cd1 or methanol dehydrogenase and other predicted eight-bladed beta-propeller domains in proteins, such as the pyrolloquinoline quinone-dependent alcohol dehydrogenase, are discussed and compared with other propeller proteins. From sequencing the nirS gene of Thiosphaera pantotropha, it is established that the amino acid sequence deduced previously in part from X-ray diffraction data at lower resolution was largely correct, as was the proposal that eight N-terminal amino acid residues were not seen in the structure. The unusual haem iron environments in both the c-type cytochrome domain, with His/His coordination, and the d1-type cytochrome domain with Tyr/His coordination are related to the functions of the redox centres.

The interaction between mood and cognitive function studied with PET

BACKGROUND

Experimentally induced depressed mood is a suggested model for retarded depression. We describe the neural response associated with induced mood and the locus of the interaction between systems mediating mood and cognitive function.

METHODS

Normal subjects performed a verbal fluency task during induced elated and depressed mood states. Regional cerebral blood flow (rCBF) was measured as an index of neural activity using Positron Emission Tomography (PET).

RESULTS

In both elated and depressed mood state rCBF was increased in lateral orbitofrontal cortex, rCBF was also increased in the midbrain in elated mood. In the depressed condition rCBF was decreased in rostral medial prefrontal cortex. Verbal fluency produced an expected increase of rCBF in left dorsolateral prefrontal, inferior frontal and premotor cortex, anterior cingulate and insula cortex bilaterally, the left supramarginal gyrus posteriorly and the thalamus. Activation in the verbal fluency task was attenuated throughout the left prefrontal, premotor and cingulate cortex and thalamus in both elated and depressed mood conditions. An attenuation of anterior cingulate activation was specific to depressed mood.

CONCLUSIONS

Alteration of mood is associated with activation of orbitofrontal cortex which may be critical to the experience of emotion. The mood induced modulation of verbal fluency induced activations is consistent with resting state findings of decreased function in these regions in depressed patients. The present data suggest that resting state rCBF profile may represent the modulation of spontaneous activity in this network by a core system that is dysfunctional in depression.

Interactions among genes regulating ovule development in Arabidopsis thaliana

The INNER NO OUTER (INO) and AINTEGUMENTA (ANT) genes are essential for ovule integument development in Arabidopsis thaliana. Ovules of ino mutants initiate two integument primordia, but the outer integument primordium forms on the opposite side of the ovule from the normal location and undergoes no further development. The inner integument appears to develop normally, resulting in erect, unitegmic ovules that resemble those of gymnosperms. ino plants are partially fertile and produce seeds with altered surface topography, demonstrating a lineage dependence in development of the testa. ant mutations affect initiation of both integuments. The strongest of five new ant alleles we have isolated produces ovules that lack integuments and fail to complete megasporogenesis. ant mutations also affect flower development, resulting in narrow petals and the absence of one or both lateral stamens. Characterization of double mutants between ant, ino and other mutations affecting ovule development has enabled the construction of a model for genetic control of ovule development. This model proposes parallel independent regulatory pathways for a number of aspects of this process, a dependence on the presence of an inner integument for development of the embryo sac, and the existence of additional genes regulating ovule development.

Evolution of mouse hepatitis virus: detection and characterization of spike deletion variants during persistent infection

High-frequency RNA recombination has been proposed as an important mechanism for generating viral deletion variants of murine coronavirus. Indeed, a number of variants with deletions in the spike glycoprotein have been isolated from persistently infected animals. However, the significance of generating and potentially accumulating deletion variants in the persisting viral RNA population is unclear. To study this issue, we evaluated the evolution of spike variants by examining the population of spike RNA sequences detected in the brains and spinal cords of mice inoculated with coronavirus and sacrificed at 4, 42, or 100 days postinoculation. We focused on the S1 hypervariable region since previous investigators had shown that this region is subject to recombination and deletion. RNA isolated from the brains or spinal cords of infected mice was rescued by reverse transcription-PCR, and the amplified products were cloned and used in differential colony hybridizations to identify individual isolates with deletions. We found that 11 of 20 persistently infected mice harbored spike deletion variants (SDVs), indicating that deletions are common but not required for persistent infection. To determine if a specific type of SDV accumulated during persistence, we sequenced 106 of the deletion isolates. We identified 23 distinct patterns of SDVs, including 5 double-deletion variants. Furthermore, we found that each mouse harbored distinct variants in its central nervous system (CNS), suggesting that SDVs are generated during viral replication in the CNS. Interestingly, mice with the most severe and persisting neurological disease harbored the most prevalent and diverse quasispecies of SDVs. Overall, these findings illustrate the complexity of the population of persisting viral RNAs which may contribute to chronic disease.

Methylosulfonomonas methylovora gen. nov., sp. nov., and Marinosulfonomonas methylotropha gen. nov., sp. nov.: novel methylotrophs able to grow on methanesulfonic acid

Two novel genera of restricted facultative methylotrophs are described; both Methylosulfonomonas and Marinosulfonomonas are unique in being able to grow on methanesulfonic acid as their sole source of carbon and energy. Five identical strains of Methylosulfonomonas were isolated from diverse soil samples in England and were shown to differ in their morphology, physiology, DNA base composition, molecular genetics, and 16S rDNA sequences from the two marine strains of Marinosulfonomonas, which were isolated from British coastal waters. The marine strains were almost indistinguishable from each other and are considered to be strains of one species. Type species of each genus have been identified and named Methylosulfonomonas methylovora (strain M2) and Marinosulfonomonas methylotropha (strain PSCH4). Phylogenetic analysis using 16S rDNA sequencing places both genera in the alpha-Proteobacteria. Methylosulfonomonas is a discrete lineage within the alpha-2 subgroup and is not related closely to any other known bacterial genus. The Marinosulfonomonas strains form a monophyletic cluster in the alpha-3 subgroup of the Proteobacteria with Roseobacter spp. and some other partially characterized marine bacteria, but they are distinct from these at the genus level. This work shows that the isolation of bacteria with a unique biochemical character, the ability to grow on methanesulfonic acid as energy and carbon substrate, has resulted in the identification of two novel genera of methylotrophs that are unrelated to any other extant methylotroph genera.

Dopamine efflux in the rat nucleus accumbens evoked by dopamine receptor stimulation in the entorhinal cortex is modulated by oestradiol and progesterone

This study compared the effects of dopamine receptor stimulation in the entorhinal cortex on dopamine release in the nucleus accumbens, measured by in vivo microdialysis in conscious Sprague-Dawley rats, with and without oestradiol and progesterone priming. Nonselective dopamine receptor stimulation with apomorphine reduced dopamine release in the nucleus accumbens, an effect which was prevented by injection of cis-flupenthixol into the entorhinal cortex. Selective D1 receptor stimulation with SKF38393 increased dopamine release, whereas selective D2 receptor stimulation with quinpirole did not affect dopamine release. Combined administration of oestradiol and progesterone potentiated the response to apomorphine and prevented the response to SKF38393. The effects of single hormone administration on the response to apomorphine suggested that the modulation was primarily due to oestradiol enhancing effects of progesterone. Experiments with high [K+] suggested these hormonal effects were exerted predominantly in the entorhinal cortex. The present experiments have demonstrated that dopaminergic modulation of transmission in a cortico-striatal loop linking temporal and prefrontal cortex is regulated by oestradiol and progesterone. Dysfunction in this system in humans may give rise to affective and cognitive symptoms which may, if initiated by a postpartum fall in oestrogen and progesterone concentrations, constitute the core pathophysiology of puerperal psychosis.

Active representation of shape and spatial location in man

Neural activity during the delay period of spatial delayed response (DR) and delayed matching (DM) tasks was investigated by positron emission tomography. A distributed cortical system was activated in each condition. The bilateral dorsolateral prefrontal cortex (DLPFC) was activated in the delay period of both tasks; activation was of higher significance on the right in the DR task and the left in the DM task, and extended to the anterolateral prefrontal cortex in the DM condition. Active representation of spatial location in the DR task was associated with co-activation of the medial and lateral parietal cortex and the extrastriate visual cortex. Active representation of shape in the DM task was associated with co-activation of medial and lateral parietal cortex and the inferior temporal cortex. Response-related activity was observed in both tasks. Activation of anterior cingulate, inferior frontal, lateral promotor and rostral inferior parietal cortex was observed in the DR condition, a task characterized by preparation of a movement to a predetermined location. In contrast, preparation to move to an undetermined location in the DM task was associated with activation predominantly in rostral SMA.

Neural systems engaged by planning: a PET study of the Tower of London task

The functional anatomy of planning was investigated using the Tower of London task. Activation was observed in a distributed network of cortical areas incorporating prefrontal, cingulate, premotor, parietal and occipital cortices. Activation in corresponding areas has been observed in visuospatial working memory tasks with the exception of the rostral prefrontal cortex. This area may be identified with the executive components of planning comprising response selection and evaluation. Enhanced neural activity in both this rostral prefrontal area and the visuospatial working memory system was associated with increased task difficulty.

Primary structure and phylogeny of the Calvin cycle enzymes transketolase and fructosebisphosphate aldolase of Xanthobacter flavus

Xanthobacter flavus, a gram-negative facultatively autotrophic bacterium, employs the Calvin cycle for the fixation of carbon dioxide. Cells grown under autotrophic growth conditions possess an Fe(2+)-dependent fructosebisphosphate (FBP) aldolase (class II) in addition to a class I FBP aldolase. By nucleotide sequencing and heterologous expression in Escherichia coli, genes encoding transketolase (EC 2.2.1.1.; CbbT) and class II FBP aldolase (EC 4.1.2.13; CbbA) were identified. A partial open reading frame encoding a protein similar to pentose-5-phosphate 3-epimerase was identified downstream from cbbA. A phylogenetic tree of transketolase proteins displays a conventional branching order. However, the class II FBP aldolase protein from X. flavus is only distantly related to that of E. coli. The autotrophic FBP aldolase proteins from X. flavus, Alcaligenes eutrophus, and Rhodobacter sphaeroides form a tight cluster, with the proteins from gram-positive bacteria as the closest relatives.

Other minds in the brain: a functional imaging study of "theory of mind" in story comprehension

The ability of normal children and adults to attribute independent mental states to self and others in order to explain and predict behaviour ("theory of mind") has been a focus of much recent research. Autism is a biologically based disorder which appears to be characterised by a specific impairment in this "mentalising" process. The present paper reports a functional neuroimaging study with positron emission tomography in which we studied brain activity in normal volunteers while they performed story comprehension tasks necessitating the attribution of mental states. The resultant brain activity was compared with that measured in two control tasks: "physical" stories which did not require this mental attribution, and passages of unlinked sentences. Both story conditions, when compared to the unlinked sentences, showed significantly increased regional cerebral blood flow in the following regions: the temporal poles bilaterally, the left superior temporal gyrus and the posterior cingulate cortex. Comparison of the "theory of mind" stories with "physical" stores revealed a specific pattern of activation associated with mental state attribution: it was only this task which produced activation in the medial frontal gyrus on the left (Brodmann's area 8). This comparison also showed significant activation in the posterior cingulate cortex. These surprisingly clear-cut findings are discussed in relation to previous studies of brain activation during story comprehension. The localisation of brain regions involved in normal attribution of mental states and contextual problem solving is feasible and may have implication for the neural basis of autism.

The mind's eye--precuneus activation in memory-related imagery

We examined brain activity associated with visual imagery at episodic memory retrieval using positron emission tomography (PET). Twelve measurements of regional cerebral blood flow (rCBF) were taken in six right-handed, healthy, male volunteers. During six measurements, they were engaged in the cued recall of imageable verbal paired associates. During the other six measurements, they recalled nonimageable paired associates. Memory performance was equalized across all word lists. The subjects' use of an increased degree of visual imagery during the recall of imageable paired associates was confirmed using subjective rating scales after each scan. Memory-related imagery was associated with significant activation of a medial parietal area, the precuneus. This finding confirms a previously stated hypothesis about the precuneus and provides strong evidence that it is a key part of the neural substate of visual imagery occurring in conscious memory recall.

Evolution of mouse hepatitis virus (MHV) during chronic infection: quasispecies nature of the persisting MHV RNA

Coronavirus infection of mice has been used extensively as a model for the study of acute encephalitis and chronic demyelination. To examine the evolution of coronavirus RNA during chronic demyelinating infection, we isolated RNA from intracerebrally inoculated mice at 4, 6, 8, 13, 20, and 42 days postinfection and used reverse transcription-polymerase chain reaction amplification methods (RT-PCR) to detect viral sequences. RNA sequences from two viral structural genes, the spike gene and the nucleocapsid gene, were detected throughout the chronic infection. In contrast, infectious virus was not detectable from brain homongenates beyond 13 days postinfection. These results indicate that coronavirus RNA persists in the brain at times when infectious virus is not detected. To determine if genetic changes were occurring during viral replication in the host, we cloned and sequenced the RT-PCR products from the spike and nucleocapsid regions and analyzed the sequences for mutations. Sequencing of the cloned products revealed that a variety of mutant forms of viral RNA persisted in the CNS, including point mutants, deletion mutants, and termination mutants. The mutations accumulated during persistent infection in both the spike and the nucleocapsid sequences, with greater than 65% of the mutations encoding amino acid changes. These results show that a diverse population or quasispecies consisting of mutant and deletion variant viral RNAs (which may not be capable of producing infectious virus particles) persists in the central nervous system of mice during chronic demyelinating infection. The implications of these results for the role of persistent viral genetic information in the pathogenesis of chronic demyelination are discussed.

Mutations associated with viral sequences isolated from mice persistently infected with MHV-JHM

Mouse hepatitis virus JHM (JHMV or MHV-4) induces subacute and chronic demyelination in rodents and has been studied as a model human demyelinating diseases, such a multiple sclerosis. However, despite intensive investigation, the state of JHMV during chronic disease is poorly understood. Using reverse transcription-polymerase chain reaction amplification (RT-PCR) to "rescue" viral RNA, we have found that JHMV-specific sequences persist for at least 787 days after intracerebral inoculation of experimental mice. Analysis of persisting viral RNA reveals that it is extensively mutated, and we hypothesize that the mutations observed reflect adaptation of the viral quasispecies to low-level intracellular replication during chronic disease.

Determinants of the p28 cleavage site recognized by the first papain-like cysteine proteinase of murine coronavirus

The murine coronavirus polymerase gene is 22 kb in length with the potential to encode a polyprotein of approximately 750 kDa. The polyprotein has been proposed to encode three proteinase domains which are responsible for the processing of the polyprotein into mature proteins. The proteolytic activity of the first proteinase domain has been characterized and resembles the papain family of cysteine proteinases. This proteinase domain acts autoproteolytically to cleave the amino terminal portion of the polymerase polyprotein, releasing a 28-kDa protein designated p28. To identify the cleavage site of this papain-like cysteine proteinase, we isolated the peptide adjacent to p28 and determined the amino terminus sequence by Edman degradation reaction. We report that proteolysis occurs between the Gly-247 and Val-248 dipeptide bond. To determine the role of the amino acid residues surrounding the cleavage site, we introduced a total of 42 site-specific mutations at the residues spanning the P5 to P3' positions and assessed the effects of the mutations on the processing of p28 in an in vitro transcription and translation system. The substitutions of Gly-247 at the P1 position or Arg-246 at the P2 position resulted in a dramatic decrease of proteolytic activity, and the mutations of Arg-243 at P5 position also led to considerable reduction in p28 cleavage. In contrast, the substitutions of amino acids Gly-244 (P4), Tyr-245 (P3), Val-248 (P1'), Lys-249 (P2'), and Pro-250 (P3') had little or no effect on the amount of p28 that was released. This work had identified Gly-247-Val-248 as the cleavage site for the release of p28, the amino-terminal protein of the murine coronavirus polymerase polyprotein. Additionally, we conclude that the Gly-247 and Arg-246 are the major determinants for the cleavage site recognition by the first papain-like cysteine proteinase of murine coronavirus.

Arabidopsis floral homeotic gene BELL (BEL1) controls ovule development through negative regulation of AGAMOUS gene (AG)

Ovules are the developmental precursors of seeds. In angiosperms the ovules are enclosed within the central floral organs, the carpels. We have identified a homeotic mutation in Arabidopsis, "bell" (bel1), which causes transformation of ovule integuments into carpels. In situ hybridization analysis shows that this mutation leads to increased expression of the carpel-determining homeotic gene AGAMOUS (AG) in the mutant ovules. Introduction of a constitutively expressed AG transgene into wild-type plants causes the ovules to resemble those of bel1 mutants. We propose that the BEL1 gene product directs normal integument development, in part by suppressing AG expression in this structure. Our results allow expansion of the current model of floral organ identity to include regulation of ovule integument identity.

Altered proteolytic processing of the polymerase polyprotein in RNA(-) temperature sensitive mutants of murine coronavirus

We examined the synthesis and processing of the polymerase polyprotein in RNA(-) temperature sensitive mutant of murine coronavirus strain A59. These temperature sensitive mutants of MHV-A59 synthesize viral RNA at the permissive temperature (33.0 degrees C), but are unable to synthesize viral RNA at the nonpermissive temperature (39.5 degrees C). The ts mutants have been mapped to five different complementation groups in the polymerase gene. The 5'-most complementation groups, Groups A and B, map to a region encoding an autoproteinase responsible for the cleavage of p28, the amino-terminal product of the polymerase polyprotein. We screened six temperature sensitive mutants to determine if there was an alteration in the proteolytic processing of the polymerase polyprotein, particularly in the cleavage of the p28 protein. Two mutants, tsNC9 and tsLA16, had altered proteolytic products at both the permissive and nonpermissive temperatures. One Group B temperature sensitive mutant, designated tsNC11, was defective in the production of p28 protein at the nonpermissive temperature. To further localize the site of the mutation in tsNC11, RNA representing the 5'-most 5.3 kb region of the polymerase gene was transfected into tsNC11-infected cells and virus production monitored. The transfected RNA was able to complement the defect in tsNC11, resulting in viral RNA synthesis and production of viral particles at the nonpermissive temperature. These results indicate that a gene product from the 5.3 kb region of gene 1 is required for coronavirus RNA synthesis.

Identification of the catalytic sites of a papain-like cysteine proteinase of murine coronavirus

The murine coronavirus mouse hepatitis virus gene 1 is expressed as a polyprotein, which is cleaved into multiple proteins posttranslationally. One of the proteins is p28, which represents the amino-terminal portion of the polyprotein and is presumably generated by the activity of an autoproteinase domain of the polyprotein (S. C. Baker, C. K. Shieh, L. H. Soe, M.-F. Chang, D. M. Vannier, and M. M. C. Lai, J. Virol. 63:3693-3699, 1989). In this study, the boundaries and the critical amino acid residues of this putative proteinase domain were characterized by deletion analysis and site-directed mutagenesis. Proteinase activity was monitored by examining the generation of p28 during in vitro translation in rabbit reticulocyte lysates. Deletion analysis defined the proteinase domain to be within the sequences encoded from the 3.6- to 4.4-kb region from the 5' end of the genome. A 0.7-kb region between the substrate (p28) and proteinase domain could be deleted without affecting the proteolytic cleavage. However, a larger deletion (1.6 kb) resulted in the loss of proteinase activity, suggesting the importance of spacing sequences between proteinase and substrate. Computer-assisted analysis of the amino acid sequence of the proteinase domain identified potential catalytic cysteine and histidine residues in a stretch of sequence distantly related to papain-like cysteine proteinases. The role of these putative catalytic residues in the proteinase activity was studied by site-specific mutagenesis. Mutations of Cys-1137 or His-1288 led to a complete loss of proteinase activity, implicating these residues as essential for the catalytic activity. In contrast, most mutations of His-1317 or Cys-1172 had no or only minor effects on proteinase activity. This study establishes that mouse hepatitis virus gene 1 encodes a proteinase domain, in the region from 3.6 to 4.4 kb from the 5' end of the genome, which resembles members of the papain family of cysteine proteinases and that this proteinase domain is responsible for the cleavage of the N-terminal peptide.

Dependence of the yield of strand breaks induced by gamma-rays in DNA on the physical conditions of exposure: water content and temperature

The induction by 60Co gamma-rays of DNA breaks, revealed by relaxation (single-strand breaks, SSBs) and linearization (double-strand breaks, DSBs) of supercoiled plasmid DNA, was measured under three irradiation conditions, the DNA being in a dry, humid, or aqueous state in the absence of oxygen, at 25 or -196 degrees C (77 K). Yields of strand breaks (3.0 x 10(-10) SSB/Gy.Da and 2.6 x 10(-11) DSB/Gy.Da) in DNA exposed to a stream of humidified nitrogen were higher than those in the dry condition (5.7 x 10(-11) SSB/Gy.Da and 3.2 x 10(-12) DSB/Gy.Da), but both these yields were markedly lower than those measured for DNA in aqueous solution at a concentration of 73 micrograms/cm3 (1.14 x 10(-7) SSB/Gy.Da and 5.4 x 10(-9) DSB/Gy.Da). Over 100-fold fewer SSBs were observed in the frozen aqueous system compared with the non-frozen liquid state, whereas in the dry and humid states, freezing did not affect the yield as much. The same trend was observed for DSBs. However, the induction of SSBs was more affected than that of DSBs by freezing in the aqueous systems. An interesting reverse relationship was observed in humid systems. The observed linearity of DSB induction with radiation dose supported a single-event mechanism. A comparison of G values for humid systems revealed that the role of bound water in radiation damage becomes significant in the nonfrozen state. Based on these and other measurements of strand breaks under different conditions, the significance of bound and free water on the yields of DNA strand breaks by gamma-rays is discussed, and the relevance of these results to the in vivo situation outlined.

Hemagglutinin-esterase-specific monoclonal antibodies alter the neuropathogenicity of mouse hepatitis virus

Some of mouse hepatitis virus strains contain an optional envelope glycoprotein, hemagglutinin-esterase (HE) protein. To understand the functional significance of this protein, monoclonal antibodies (MAbs) specific for this protein were generated and used for passive immunization of mice. None of these MAbs showed any virus-neutralizing activity in vitro; however, mice passively immunized with the purified MAbs were protected from lethal infection by the JHM strain of mouse hepatitis virus. Passive immunization altered the pathogenicity such that the virus caused subacute and chronic demyelination instead of acute lethal encephalitis. Virus titers in the brains of the immunized mice were significantly lower than those for the nonimmunized control mice, suggesting that the virus replication or spread was inhibited. In addition, histopathological analysis indicated that the spread of virus in the brain and spinal cord was significantly inhibited in the immunized mice. Furthermore, the mononuclear cell infiltration in the immunized mice appeared earlier than in the nonimmunized mice, suggesting that the exogenous antibody might have activated host immune responses, and thus facilitated clearance of the virus or virus-infected cells. The same protective effects were observed for both JHM(2) and JHM(3) viruses, which expressed different amounts of the HE protein. In contrast, mice infected with At11f, a variant of JHM which does not express the HE protein, were not protected by these MAbs, suggesting that protection was mediated by the specific interaction between the MAb and the HE protein. Thus, the mechanism of protection by the exogenous HE-specific MAbs may represent the early activation of innate immune mechanisms in response to the interaction between the MAbs and the HE protein.

An in vitro system for the leader-primed transcription of coronavirus mRNAs

We have developed an in vitro transcription system which can utilize exogenous leader RNA for mouse hepatitis virus (MHV) 'leader-primed' mRNA transcription. Cytoplasmic extracts containing viral proteins and template RNA were prepared by lysolecithin permeabilization of MHV-infected cells. Synthetic leader RNA which differed in sequence from the endogenous leader RNA was added to the extracts and demonstrated to be incorporated into MHV mRNAs. Irrespective of the size of leader RNAs added, the exogenous leader RNA was joined to the endogenous mRNA at the same site, which corresponds to a UCUAA pentanucleotide repeat region. Only leader RNAs containing the pentanucleotide sequences could be utilized for transcription. Mismatches between the intergenic site and the exogenous leader sequence within the pentanucleotide repeat region were corrected in the in vitro system. This in vitro system thus established a novel mechanism of leader-primed transcription using exogenous RNA in trans, and suggests the involvement of a specific ribonuclease activity during coronavirus mRNA synthesis.

Characterization of hepatitis delta antigen: specific binding to hepatitis delta virus RNA

It has previously been shown that human hepatitis virus delta antigen has an RNA-binding activity (Chang et al., J. Virol. 62:2403-2410, 1988). In the present study, the specificity of such an RNA-protein interaction was demonstrated by expressing various domains of the delta antigen in Escherichia coli as TrpE fusion proteins and testing their RNA-binding activities in a Northwestern protein-RNA immunoblot assay and RNA gel mobility shift assay. Hepatitis delta virus (HDV) RNA bound specifically to the delta antigen in the presence of an excess amount of unrelated RNAs and a relatively high salt concentration. Both genome- and antigenome-sense HDV RNAs and at least two different regions of HDV genomic RNA bound to the delta antigen. Surprisingly, these two different regions of HDV genomic RNA could compete with each other for delta antigen binding, although they do not have common nucleotide sequences. In contrast, this binding could not be competed with by other viral or cellular RNA. Since both the genomic and antigenomic HDV RNAs had strong intramolecular complementary sequences, these results suggest that the binding of delta antigen is probably specific for a secondary structure unique to the HDV RNA. By expressing different subdomains of the delta antigen, we found that the middle one-third of delta antigen was responsible for binding HDV RNA. Neither the N-terminal nor the C-terminal domain bound HDV RNA. Binding between the delta antigen and HDV RNA was also demonstrated within the HDV particles isolated from the plasma of a human delta hepatitis patient. This in vivo binding resisted treatment with 0.1% sodium dodecyl sulfate and 0.5% Nonidet P-40. In addition, we showed that the antiserum from a human patient with delta hepatitis reacted with all three subdomains of the delta antigen, indicating that all of the domains are immunogenic in vivo. These studies demonstrated the specific interaction between delta antigen and HDV RNA.