Development and Validation of Three Automated High-Throughput Molecular Tests to Detect Monkeypox Virus Infections

BACKGROUND

The 2022 outbreak of the clade IIb monkeypox virus and subsequent global spread lead to an urgent need for the development of high-throughput, sensitive, and reproducible diagnostic tests.

METHODS

We developed 3 assays to detect monkeypox virus, 2 (MPXV+ and MPXV) for m2000 RealTime and 1 (MPXV) for Alinity m platforms. Dual targets in E9L and B6R (MPXV+) and J2L and B7R (MPXV) increased mutation resistance. In silico prediction indicates MPXV+ cross-reactivity with orthopox viruses and specific monkeypox virus detection with MPXV.

RESULTS

m2000 RealTime MPXV+ and MPXV assay sensitivity was determined to be 3.2 plaque-forming units/mL using a reference virus culture diluted into universal transport medium (UTM). Alinity m MPXV lower limit of detection was 200 copies/mL using monkeypox virus plasmids in pooled UTM matrix. m2000 RealTime MPXV+ and MPXV assays were validated with lesion swabs in UTM and 1:1 saliva to UTM mixtures. Commercially available and remnant clinical lesion specimens in UTM were tested with RealTime MPXV+, RealTime MPXV and Alinity m MPXV assays and demonstrated high agreement to known mpox (MPX)-positive specimens.

CONCLUSIONS

RealTime MPXV+, RealTime MPXV, and Alinity MPXV are high throughput and sensitive assays used for the detection of monkeypox virus. These assays maybe useful during MPX outbreaks.

Purifying selection decreases the potential for Bangui orthobunyavirus outbreaks in humans

Pathogens carried by insects, such as bunyaviruses, are frequently transmitted into human populations and cause diseases. Knowing which spillover events represent a public health threat remains a challenge. Metagenomic next-generation sequencing (mNGS) can support infectious disease diagnostics by enabling the detection of any pathogen from clinical specimens. mNGS was performed on blood samples to identify potential viral coinfections in human immunodeficiency virus (HIV)-positive individuals from Kinshasa, the Democratic Republic of the Congo (DRC), participating in an HIV diversity cohort study. Time-resolved phylogenetics and molecular assay development assisted in viral characterization. The nearly complete genome of a novel orthobunyavirus related to Nyangole virus, a virus previously identified in neighboring Uganda, was assembled from a hepatitis B virus–positive patient. A quantitative polymerase chain reaction assay was designed and used to screen >2,500 plasma samples from Cameroon, the DRC, and Uganda, failing to identify any additional cases. The recent sequencing of a US Center for Disease Control Arbovirus Reference Collection revealed that this same virus, now named Bangui virus, was first isolated in 1970 from an individual in the Central African Republic. Time-scaled phylogenetic analyses of Bangui with the related Anopheles and Tanga serogroup complexes indicate that this virus emerged nearly 10,000 years ago. Pervasive and episodic models further suggest that this virus is under purifying selection and that only distant common ancestors were subject to positive selection events. This study represents only the second identification of a Bangui virus infection in over 50 years. The presumed rarity of Bangui virus infections in humans can be explained by its constraint to an avian host and insect vector, precluding efficient transmission into the human population. Our results demonstrate that molecular phylogenetic analyses can provide insights into the threat posed by novel or re-emergent viruses identified by mNGS.

Circulating Pregenomic Hepatitis B Virus RNA Is Primarily Full-length in Chronic Hepatitis B Patients Undergoing Nucleos(t)ide Analogue Therapy

Hepatitis B virus RNA is detectable in the serum of infected patients; however, the RNA species has been questioned. We tested 1827 specimens using a quantitative dual-target quantitative polymerase chain reaction assay and determined that full-length pregenomic RNA is the primary source. These results clarify the major identity of circulating HBV RNA species.

Hepatitis B Virus Serum DNA andRNA Levels in Nucleos(t)ide Analog-Treated or Untreated Patients During Chronic and Acute Infection

Treatment of chronic hepatitis B (CHB) patients with nucleos(t)ide analogs (NAs) suppresses hepatitis B virus (HBV) DNA synthesis but does not affect synthesis of HBV pregenomic RNA (pgRNA). Hepatitis B virus pgRNA is detectable in the serum during NA treatment and has been proposed as a marker of HBV covalently closed circular DNA activity within the infected hepatocyte. We developed an automated assay for the quantification of serum HBV pgRNA using a dual-target real-time quantitative PCR approach on the Abbott m2000sp/rt system. We demonstrate accurate detection and quantification of serum HBV RNA. Hepatitis B virus DNA was quantified using the Abbott RealTime HBV viral load assay. We further compared serum nucleic acid levels and kinetics in HBV-positive populations. Samples included on-therapy CHB samples (n = 16), samples (n = 89) from 10 treatment naïve CHB subjects receiving 12 weeks of NA treatment with 8-week follow-up, hepatitis B surface antigen-positive blood donor samples (n = 102), and three seroconversion series from plasmapheresis donors (n = 79 samples). Conclusion: During NA treatment of CHB subjects, we observed low correlation of HBV DNA to pgRNA levels; pgRNA concentration was generally higher than HBV DNA concentrations. In contrast, when NA treatment was absent we observed serum pgRNA at concentrations that correlated to HBV DNA and were approximately 2 log lower than HBV DNA. Importantly, we observe this trend in untreated subject samples from both chronic infections and throughout seroconversion during acute infection. Results demonstrate that the presence of pgRNA in serum is part of the HBV lifecycle; constant relative detection of pgRNA and HBV DNA in the serum is suggestive of a linked mechanism for egress for HBV DNA or pgRNA containing virions.

Identification of a putative novel genotype 3/rabbit hepatitis E virus (HEV) recombinant

Hepatitis E virus (HEV) is a viral pathogen transmitted by the fecal-oral route and is a major cause of waterborne acute hepatitis in many developing countries. In addition to infecting humans, HEV has been identified in swine, wild boars, rabbits and other mammals; with swine and wild boars being main reservoirs for zoonotic transmission of HEV. There are four major HEV genotypes known to infect humans; genotypes 1 (HEV-1) and 2 (HEV-2) are restricted to humans, and genotypes 3 (HEV-3) and 4 (HEV-4) are zoonotic. Herein, three human HEV strains originating in France were sequenced and near full-length genomes were characterized. Phylogenetic analysis showed that two strains were genotype 3 and closely grouped (a 100% bootstrap value) with subtype 3i reference strains. In percent nucleotide identities, these two strains were 94% identical to each other, 90–93% identical to subtype 3i strains, 82–86% identical to other HEV-3, and 77–79% identical to rabbit HEV strains excluding the two divergent strains KJ013414 and KJ013415 (74%); these two strains were less than 77% identical to strains of HEV genotypes 1, 2 and 4. The third strain was found distinct from any known HEV strains in the database, and located between the clusters of HEV-3 and rabbit HEV strains. This unique strain was 74–75% identical to HEV-1, 73% to HEV-2, 81–82% to HEV-3, 77–79% to rabbit HEV again excluding the two divergent strains KJ013414 and KJ013415 (74%), and 74–75% to HEV-4, suggesting a novel unclassified strain associated with HEV-3 and rabbit HEV. SimPlot and BootScan analyses revealed a putative recombination of HEV-3 and rabbit HEV sequences at four breakpoints. Phylogenetic trees of the five fragments of the genome confirmed the presence of two HEV-3 derived and three unclassified sequences. Analyses of the amino acid sequences of the three open reading frames (ORF1-3) encoded proteins of these three novel strains showed that some amino acid residues specific to rabbit HEV strains were found solely in this unclassified strain but not in the two newly identified genotype 3i strains. The results obtained by SimPlots, BootScans, phylogenetic analyses, and amino acid sequence comparisons in this study all together appear to suggest that this novel unclassified strain is likely carrying a mosaic genome derived from HEV-3 and rabbit HEV sequences, and is thus designated as a putative genotype 3/rabbit HEV recombinant.

Development and performance of prototype serologic and molecular tests for hepatitis delta infection

Worldwide, an estimated 5% of hepatitis B virus (HBV) infected people are coinfected with hepatitis delta virus (HDV). HDV infection leads to increased mortality over HBV mono-infection, yet HDV diagnostics are not widely available. Prototype molecular (RNA) and serologic (IgG) assays were developed for high-throughput testing on the Abbott m2000 and ARCHITECT systems, respectively. RNA detection was achieved through amplification of a ribozyme region target, with a limit of detection of 5 IU/ml. The prototype serology assay (IgG) was developed using peptides derived from HDV large antigen (HDAg), and linear epitopes were further identified by peptide scan. Specificity of an HBV negative population was 100% for both assays. A panel of 145 HBsAg positive samples from Cameroon with unknown HDV status was tested using both assays: 16 (11.0%) had detectable HDV RNA, and 23 (15.7%) were sero-positive including the 16 HDV RNA positive samples. Additionally, an archival serial bleed panel from an HDV superinfected chimpanzee was tested with both prototypes; data was consistent with historic testing data using a commercial total anti-Delta test. Overall, the two prototype assays provide sensitive and specific methods for HDV detection using high throughput automated platforms, allowing opportunity for improved diagnosis of HDV infected patients.

Utility of Metagenomic Next-Generation Sequencing for Characterization of HIV and Human Pegivirus Diversity

Given the dynamic changes in HIV-1 complexity and diversity, next-generation sequencing (NGS) has the potential to revolutionize strategies for effective HIV global surveillance. In this study, we explore the utility of metagenomic NGS to characterize divergent strains of HIV-1 and to simultaneously screen for other co-infecting viruses. Thirty-five HIV-1-infected Cameroonian blood donor specimens with viral loads of >4.4 log₁₀ copies/ml were selected to include a diverse representation of group M strains. Random-primed NGS libraries, prepared from plasma specimens, resulted in greater than 90% genome coverage for 88% of specimens. Correct subtype designations based on NGS were concordant with sub-region PCR data in 31 of 35 (89%) cases. Complete genomes were assembled for 25 strains, including circulating recombinant forms with relatively limited data available (7 CRF11_cpx, 2 CRF13_cpx, 1 CRF18_cpx, and 1 CRF37_cpx), as well as 9 unique recombinant forms. HPgV (formerly designated GBV-C) co-infection was detected in 9 of 35 (25%) specimens, of which eight specimens yielded complete genomes. The recovered HPgV genomes formed a diverse cluster with genotype 1 sequences previously reported from Ghana, Uganda, and Japan. The extensive genome coverage obtained by NGS improved accuracy and confidence in phylogenetic classification of the HIV-1 strains present in the study population relative to conventional sub-region PCR. In addition, these data demonstrate the potential for metagenomic analysis to be used for routine characterization of HIV-1 and identification of other viral co-infections.

A cloud-compatible bioinformatics pipeline for ultrarapid pathogen identification from next-generation sequencing of clinical samples

Unbiased next-generation sequencing (NGS) approaches enable comprehensive pathogen detection in the clinical microbiology laboratory and have numerous applications for public health surveillance, outbreak investigation, and the diagnosis of infectious diseases. However, practical deployment of the technology is hindered by the bioinformatics challenge of analyzing results accurately and in a clinically relevant timeframe. Here we describe SURPI (“sequence-based ultrarapid pathogen identification”), a computational pipeline for pathogen identification from complex metagenomic NGS data generated from clinical samples, and demonstrate use of the pipeline in the analysis of 237 clinical samples comprising more than 1.1 billion sequences. Deployable on both cloud-based and standalone servers, SURPI leverages two state-of-the-art aligners for accelerated analyses, SNAP and RAPSearch, which are as accurate as existing bioinformatics tools but orders of magnitude faster in performance. In fast mode, SURPI detects viruses and bacteria by scanning data sets of 7–500 million reads in 11 min to 5 h, while in comprehensive mode, all known microorganisms are identified, followed by de novo assembly and protein homology searches for divergent viruses in 50 min to 16 h. SURPI has also directly contributed to real-time microbial diagnosis in acutely ill patients, underscoring its potential key role in the development of unbiased NGS-based clinical assays in infectious diseases that demand rapid turnaround times.

In-depth investigation of archival and prospectively collected samples reveals no evidence for XMRV infection in prostate cancer

XMRV, or xenotropic murine leukemia virus (MLV)-related virus, is a novel gammaretrovirus originally identified in studies that analyzed tissue from prostate cancer patients in 2006 and blood from patients with chronic fatigue syndrome (CFS) in 2009. However, a large number of subsequent studies failed to confirm a link between XMRV infection and CFS or prostate cancer. On the contrary, recent evidence indicates that XMRV is a contaminant originating from the recombination of two mouse endogenous retroviruses during passaging of a prostate tumor xenograft (CWR22) in mice, generating laboratory-derived cell lines that are XMRV-infected. To confirm or refute an association between XMRV and prostate cancer, we analyzed prostate cancer tissues and plasma from a prospectively collected cohort of 39 patients as well as archival RNA and prostate tissue from the original 2006 study. Despite comprehensive microarray, PCR, FISH, and serological testing, XMRV was not detected in any of the newly collected samples or in archival tissue, although archival RNA remained XMRV-positive. Notably, archival VP62 prostate tissue, from which the prototype XMRV strain was derived, tested negative for XMRV on re-analysis. Analysis of viral genomic and human mitochondrial sequences revealed that all previously characterized XMRV strains are identical and that the archival RNA had been contaminated by an XMRV-infected laboratory cell line. These findings reveal no association between XMRV and prostate cancer, and underscore the conclusion that XMRV is not a naturally acquired human infection.

Absence of XMRV and closely related viruses in primary prostate cancer tissues used to derive the XMRV-infected cell line 22Rv1

The 22Rv1 cell line is widely used for prostate cancer research and other studies throughout the world. These cells were established from a human prostate tumor, CWR22, that was serially passaged in nude mice and selected for androgen independence. The 22Rv1 cells are known to produce high titers of xenotropic murine leukemia virus-related virus (XMRV). Recent studies suggested that XMRV was inadvertently created in the 1990's when two murine leukemia virus (MLV) genomes (pre-XMRV1 and pre-XMRV-2) recombined during passaging of the CWR22 tumor in mice. The conclusion that XMRV originated from mice and not the patient was based partly on the failure to detect XMRV in early CWR22 xenografts. While that deduction is certainly justified, we examined the possibility that a closely related virus could have been present in primary tumor tissue. Here we report that we have located the original prostate tumor tissue excised from patient CWR22 and have assayed the corresponding DNA by PCR and the tissue sections by fluorescence in situ hybridization for the presence of XMRV or a similar virus. The primary tumor tissues lacked mouse DNA as determined by PCR for intracisternal A type particle DNA, thus avoiding one of the limitations of studying xenografts. We show that neither XMRV nor a closely related virus was present in primary prostate tissue of patient CWR22. Our findings confirm and reinforce the conclusion that XMRV is a recombinant laboratory-generated mouse virus that is highly adapted for human prostate cancer cells.

No evidence of murine-like gammaretroviruses in CFS patients previously identified as XMRV-infected

Members of the gammaretroviruses--such as murine leukemia viruses (MLVs), most notably XMRV [xenotropic murine leukemia virus (X-MLV)-related virus--have been reported to be present in the blood of patients with chronic fatigue syndrome (CFS). We evaluated blood samples from 61 patients with CFS from a single clinical practice, 43 of whom had previously been identified as XMRV-positive. Our analysis included polymerase chain reaction and reverse transcription polymerase chain reaction procedures for detection of viral nucleic acids and assays for detection of infectious virus and virus-specific antibodies. We found no evidence of XMRV or other MLVs in these blood samples. In addition, we found that these gammaretroviruses were strongly (X-MLV) or partially (XMRV) susceptible to inactivation by sera from CFS patients and healthy controls, which suggested that establishment of a successful MLV infection in humans would be unlikely. Consistent with previous reports, we detected MLV sequences in commercial laboratory reagents. Our results indicate that previous evidence linking XMRV and MLVs to CFS is likely attributable to laboratory contamination.

Characterization of antibodies elicited by XMRV infection and development of immunoassays useful for epidemiologic studies

Background

Xenotropic Murine Leukemia Virus-related Virus (XMRV) is a human gammaretrovirus recently identified in prostate cancer tissue and in lymphocytes of patients with chronic fatigue syndrome. To establish the etiologic role of XMRV infection in human disease requires large scale epidemiologic studies. Development of assays to detect XMRV-specific antibodies would greatly facilitate such studies. However, the nature and kinetics of the antibody response to XMRV infection have yet to be determined.

Results

Three rhesus macaques were infected with XMRV to determine the dynamics of the antibody responses elicited by infection with XMRV. All macaques developed antibodies to XMRV during the second week of infection, and the predominant responses were to the envelope protein gp70, transmembrane protein p15E, and capsid protein p30. In general, antibody responses to gp70 and p15E appeared early with higher titers than to p30, especially in the early period of seroconversion. Antibodies to gp70, p15E and p30 persisted to 158 days and were substantially boosted by re-infection, thus, were identified as useful serologic markers. Three high-throughput prototype assays were developed using recombinant proteins to detect antibodies to these viral proteins. Both gp70 and p15E prototype assays demonstrated 100% sensitivity by detecting all Western blot (WB) positive serial bleeds from the XMRV-infected macaques and good specificity (99.5-99.9%) with blood donors. Seroconversion sensitivity and specificity of the p30 prototype assay were 92% and 99.4% respectively.

Conclusions

This study provides the first demonstration of seroconversion patterns elicited by XMRV infection. The nature and kinetics of antibody responses to XMRV in primates were fully characterized. Moreover, key serologic markers useful for detection of XMRV infection were identified. Three prototype immunoassays were developed to detect XMRV-specific antibodies. These assays demonstrated good sensitivity and specificity; thus, they will facilitate large scale epidemiologic studies of XMRV infection in humans.

Near full-length genome characterization of an HIV type 1 CRF25_cpx strain from Cameroon

Recombinant forms of HIV-1 contribute significantly to the ongoing epidemic. In the present study, we characterized the near full-length genome of one candidate HIV-1 CRF25_cpx strain originating in Cameroon, 06CM-BA-040. Viral RNA was extracted from plasma, and the genome was obtained using RT-PCR amplification to generate 10 overlapping fragments. Bootscanning, recombination breakpoint analysis, and phylogenetic trees confirmed that 06CM-BA-040 had a genomic structure consistent with two available CRF25_cpx reference sequences. The CRF25_cpx mosaic composition consisted of nine segments derived from subtypes A and G as well as unclassified (U) regions. Subtype G and CRF25_cpx clusters diverged from each other with long branch lengths but were distinct from other known subtypes with high bootstrap support (94%). The epidemiological significance of CRF25_cpx strains is unknown; however, the availability of additional genomic sequences will improve our understanding of the overall genetic diversity within this recombinant form of HIV-1.

Thermodynamically modulated partially double-stranded linear DNA probe design for homogeneous real-time PCR

Real-time PCR assays have recently been developed for diagnostic and research purposes. Signal generation in real-time PCR is achieved with probe designs that usually depend on exonuclease activity of DNA polymerase (e.g. TaqMan probe) or oligonucleotide hybridization (e.g. molecular beacon). Probe design often needs to be specifically tailored either to tolerate or to differentiate between sequence variations. The conventional probe technologies offer limited flexibility to meet these diverse requirements. Here, we introduce a novel partially double-stranded linear DNA probe design. It consists of a hybridization probe 5′-labeled with a fluorophore and a shorter quencher oligo of complementary sequence 3′-labeled with a quencher. Fluorescent signal is generated when the hybridization probe preferentially binds to amplified targets during PCR. This novel class of probe can be thermodynamically modulated by adjusting (i) the length of hybridization probe, (ii) the length of quencher oligo, (iii) the molar ratio between the two strands and (iv) signal detection temperature. As a result, pre-amplification signal, signal gain and the extent of mismatch discrimination can be reliably controlled and optimized. The applicability of this design strategy was demonstrated in the Abbott RealTime HIV-1 assay.

Partially double-stranded linear DNA probes: novel design for sensitive detection of genetically polymorphic targets

Genetically polymorphic targets present a significant challenge to the reliability of detection and quantification by nucleic acid-based assays. A probe system with enhanced mismatch tolerance would be advantageous for such applications. The present study introduces a novel class of DNA probes, designated as partially double-stranded linear probes, composed of a long target-specific strand 5' labeled with a fluorophore and a markedly shorter quencher strand, complementary to the 5' end of the target-specific strand, that is 3' end-labeled with a quencher moiety. The utility of this probe system for sensitive detection of amplification products was demonstrated in a real-time PCR format. Comparison of multiple partially double-stranded linear probe combinations revealed that increased asymmetry in strand length was associated with improved mismatch tolerance. Notably, for a 45-mer/11-mer combination, the difference in threshold cycle values obtained for a perfectly matched target and one containing six mismatches was <1.5 cycles. The capacity for superior mismatch tolerance, ease of design, simplicity and flexibility of application are characteristics that make this new class of probes a desirable alternative for homogeneous detection of targets with a high level of genetic heterogeneity.

Near full-length genome characterization of three additional HIV type 1 CRF13_cpx strains from Cameroon

Recombinant forms of HIV-1 contribute significantly to the ongoing epidemic. In the present study, we characterized the near full-length genomes of three candidate HIV-1 CRF13_cpx strains originating in Cameroon, 04CM-173-9, 04CM-632-28, and 02CM-A1394. Bootscanning, recombination breakpoint analysis, and phylogenetic trees confirmed similar genomic structures with identical breakpoint positions compared to the three available CRF13_cpx sequences. The candidate and reference sequences formed a distinct cluster well separated from other group M subtypes and had a mosaic structure derived from subtypes A1, G, J, and CRF01_AE. The similarity in genomic composition and position of recombination breakpoints suggest that these isolates share a common ancestor. The epidemiological significance of CRF13_cpx strains in Cameroon is unknown; however, the availability of three additional genomic sequences will improve our understanding of the overall genetic diversity within this recombinant form of HIV-1.

HIV global surveillance: foundation for retroviral discovery and assay development

The high level of HIV genetic diversity has important implications for screening, diagnostic testing and patient monitoring. Continued diversification and global redistribution of HIV groups, subtypes and recombinants make it imperative that serological and molecular assays be designed and evaluated to ensure reliable performance on all HIV infections. Recognizing the importance of this issue, we initiated a comprehensive program to monitor global diversification of HIV, search for newly emerging variants, assemble large-volume panels of genetically and geographically diverse strains, and develop strategies to determine the impact of HIV diversity on assays used for detecting and monitoring HIV infection. Efforts to identify and characterize rare and emerging HIV strains have lead to the identification of HIV-1 group O, group N, and dual infections of groups M and O. A panel of plasma specimens was established that includes specimens collected from 12 countries in Africa, Asia, Europe, and South America; the panel comprises infections due to HIV-1 group M subtypes A, B, C, D, F, and G, as well as CRF01, CRF02, and unique recombinant forms, group N, and group O. Serological and molecular characterization of this unique panel has provided vital sequence data to support assay development and an invaluable source of well-defined specimens to evaluate and compare assay performance. The ability to address the challenge posed by ongoing evolution of HIV and the emergence of new variants requires continued surveillance of global HIV strain diversity, a sound scientific foundation for assay development, and suitable panels to evaluate and validate assay performance.

Predator-Labeling Effect on Byssus Production in Marine Mussels Perna viridis (L.) and Brachidontes variabilis (Krauss)

Mussels Perna viridis and Brachidontes variabilis were exposed to chemical cues from the predatory crab Thalamita danae maintained on different diets, and byssal thread production of the mussels was studied. P. viridis produced the highest number as well as the thickest and longest byssal threads when they were exposed to crabs maintained on a diet of P. viridis as compared with those exposed to crabs maintained on a diet of the top shell Monodonta labio, the rock oyster Saccostrea cucullata, or crabs that were starved. For B. variabilis, results were similar, in that a diet containing B. variabilis elicited the greatest response as compared with other treatments. This indicates that the mussels were able to discriminate chemical cues released from predators maintained on different diets, and respond accordingly to the level of predation risk. By increasing the strength of byssal attachment as a defensive trait, the chance of being dislodged and consumed by crabs is reduced. As energy cost involved in the induction of an antipredatory response is considerable, this defensive trait seems to be an advantage to the mussels in enhancing efficiency. The short response time in byssal thread production allows the mussels to increase resistance against predation by crabs at the time when predation pressure is the highest in a tidal cycle.

Netrin receptor deficient mice exhibit functional reorganization of dopaminergic systems and do not sensitize to amphetamine

Netrins are guidance cues that play a fundamental role in organizing the developing brain. The netrin receptor, DCC (deleted in colorectal cancer), is highly expressed by dopaminergic (DA) neurons. DCC may therefore participate in the organization of DA circuitry during development and also influence DA function in the adult. Here we show that adult dcc heterozygous mice exhibit a blunted behavioral response to the indirect DA agonist amphetamine and do not develop sensitization to its effects when treated repeatedly. These behavioral alterations are associated with profound changes in DA function. In the medial prefrontal cortex, dcc heterozygotes exhibit increased tyrosine hydroxylase (TH) protein levels and dramatic increases in basal concentrations of DA and DA metabolites. In contrast, in the nucleus accumbens, dcc heterozygotes show no changes in either TH or DA levels, but exhibit decreased concentrations of DA metabolites, suggesting reduced DA activity. In addition, dcc heterozygous mice exhibit a small, but significant reduction in total number of TH-positive neurons in midbrain DA cell body regions. These results demonstrate for the first time that alterations in dcc expression lead to selective changes in DA function and, in turn, to differences in DA-related behaviors in adulthood. These findings raise the possibility that changes in dcc function early in life are implicated in the development of DA dysregulation observed in certain psychiatric disorders, such as schizophrenia, or following chronic use of drugs of abuse.

Naturally occurring sequence polymorphisms within HIV type 1 group O protease

Mutations within the protease gene associated with reduced susceptibility to protease inhibitors have been well documented for HIV-1 group M subtype B strains. In contrast, limited genotypic and phenotypic information is available for the genetically diverse HIV-1 group O strains. Preexisting resistance-associated polymorphisms have the potential to contribute to a poor virological response to antiviral drug treatment in group O-infected patients. In the present study, the protease genes of 28 protease inhibitor-naive HIV-1 group O-infected patients were analyzed to identify any naturally occurring amino acid polymorphisms associated with drug resistance. Comparison of the consensus group O protease sequence with subtype B of group M indicated that both groups have almost identical sequences in the protease active site, the flap and the substrate-binding site. Analysis of the 28 individual protease sequences revealed polymorphisms at 34% of the positions within the protease gene, but no primary mutations associated with protease inhibitor resistance. In contrast, each of the strains harbored multiple secondary or accessory mutations associated with resistance to protease inhibitors in group M viruses. Residues 10I, 15V, 36I, 41K, 62V, 63T/A/K/I, 64V, 71V, and 93L were identified in most strains. The presence of multiple natural sequence polymorphisms associated with drug resistance in the protease gene of group O viruses may contribute to a more rapid emergence of drug resistance phenotype and treatment failure in group O-infected patients.

GABA promotes survival but not proliferation of parvalbumin-immunoreactive interneurons in rodent neostriatum: an in vivo study with stereology

Amino-acid neurotransmitters regulate a wide variety of developmental processes in the mammalian CNS including neurogenesis, cell migration, and apoptosis. In order to investigate the role of GABA in early development of forebrain interneurons, we determined the survival of parvalbumin-immunoreactive GABAergic interneurons in the adult rat striatum following prenatal exposure to either GABA(A) receptor agonist or antagonist. Unbiased stereology was used to quantify parvalbumin-immunoreactive neuron number in the neostriatum of adult rats exposed to the drugs in utero, and the results were compared to pair-fed or vehicle controls. Embryos were exposed to the GABA(A) antagonist (bicuculline) or agonist (muscimol) during previously defined proliferative or post-proliferative periods for parvalbumin-immunoreactive interneurons. Unbiased stereology using the optical fractionator was used to estimate the total number of parvalbumin-immunoreactive neurons in neostriatum of experimental and control rats. No significant alteration in parvalbumin-immunoreactive neuron number was observed in rats treated with either bicuculline (1 or 2mg/kg/day) or muscimol (1mg/kg/day) during the proliferative phase. Administration of bicuculline during the post-proliferative phase significantly reduced parvalbumin-immunoreactive neuron number in the neostriatum. A concomitant decrease in neostriatal volume was also observed, suggesting that the effect is not restricted to parvalbumin-immunoreactive interneurons. Positional analysis revealed loss of normal regional distribution gradients for parvalbumin-immunoreactive neurons in neostriatum of rats exposed to bicuculline in the embryonic post-proliferative phase. This data collectively suggests that GABA promotes survival but not proliferation of parvalbumin-immunoreactive progenitors. GABA may also promote migration of subpopulations of interneurons that ultimately populate the ventral telencephalon.

Determination of plasma viral load in HIV-1 infection by quantitative competitive polymerase chain reaction

OBJECTIVES

To better characterize viral load profiles through the course of HIV-1 disease and in response to treatment, and to further evaluate quantitative competitive polymerase chain reaction for measurement of viral load, we extended our comparative evaluation of this and other viral load measurements to a total of 118 patients, representing all stages of HIV-1 disease.

DESIGN

For cross-sectional analysis across the spectrum of HIV-1 disease, plasma viral load was evaluated in 112 HIV-1-infected patients by quantitative competitive polymerase chain reaction analysis, plasma p24 antigen assay, plasma immune complex-dissociated p24 antigen assay and an endpoint dilution viral culture. Longitudinal specimens from six additional patients were analyzed, extending from the time of presentation with symptomatic acute HIV-1 infection through up to more than 2 years of follow-up. Longitudinal specimens were also studied for three patients over the period of initiation of zidovudine treatment, for 6 weeks of treatment and following temporary withdrawal of the treatment.

METHODS

All measurement techniques were assessed in replicate aliquots of plasma.

RESULTS

Quantitative competitive polymerase chain reaction was the most sensitive measure of viral load, and was best correlated with CD4+ T-cell counts. In longitudinally studied patients, this technique also allowed measurement of plasma virus levels throughout the period of follow-up, even when culture and p24 assays became negative following resolution of acute HIV-1 infection. The quantitative competitive polymerase chain reaction was also able to detect rapid and substantial changes in viral load associated with initiation and temporary withdrawal of antiviral treatment.

CONCLUSIONS

The quantitative competitive polymerase chain reaction is promising as a sensitive and accurate method for measuring plasma viral load in HIV-1-infected patients, and is useful for following changes in viral load over the natural history of infection and following treatment intervention. The technique is particularly useful for patients with > 200 x 10(6) CD4+ T cells/l, in whom other viral markers are typically negative.

(2,3)-alpha-Methylenepenams: synthesis and in vitro activity

A series of alpha-methylene penicillins was synthesized and SAR were studied. The alpha-isomers were found to be chemically reactive and biologically active in contrast to the beta-isomers. In addition, the alpha-isomers have broader spectrum of in vitro activity than the corresponding penicillins. Generally, the alpha-isomers are more active against gram-negative bacteria than the corresponding penicillins, but slightly weaker in potency towards gram-positive organisms.

A new device for blockout procedures in rotational path removable partial dentures

The rationale of a rotation axis is discussed and on this basis a blockout device is designed for rotational path removable partial dentures. This device has three basic components, which are (1) the acrylic resin block, (2) the rotation axis, and (3) the functional part. In the blockout procedures for removable partial dentures with tilted mandibular molars, the rotation axis of the prosthesis is first localized by the blockout device. A knife edge, made of Duralay resin that corresponds to the survey lines of teeth to be used as supports, is constructed and is joined to the functional part of the blockout device. Blockout regions are determined by the rotational movement of the Duralay resin knife edge along the rotation axis of the blockout device. In addition to the function of blockout, the device can also be used to analyze diagnostic casts for critical undercuts. Internal and external types of blockout devices are also discussed.

High levels of HIV-1 in plasma during all stages of infection determined by competitive PCR

Quantitative competitive polymerase chain reaction (QC-PCR) methods were used to quantify virion-associated human immunodeficiency virus type-1 (HIV-1) RNA in plasma from 66 patients with Centers for Disease Control stage I to IVC1 infection. HIV-1 RNA, ranging from 100 to nearly 22,000,000 copies per milliliter of plasma (corresponding to 50 to 11,000,000 virions per milliliter), was readily quantified in all subjects, was significantly associated with disease stage and CD4+ T cell counts, and decreased by as much as 235-fold with resolution of primary infection or institution of antiretroviral therapy. Plasma virus levels determined by QC-PCR correlated with, but exceeded by an average of 60,000-fold, virus titers measured by endpoint dilution culture. Quantitation of HIV-1 in plasma by QC-PCR may be useful in assessing the efficacy of antiretroviral agents, especially in early stage disease when conventional viral markers are often negative.

Quantitative competitive polymerase chain reaction for accurate quantitation of HIV DNA and RNA species

Inherent features of the PCR make this procedure suboptimal for quantitative applications. For typical clinical specimens, the absolute amount of product derived from PCR does not always bear a consistent relationship to the amount of target sequence present at the start of the reaction. Competitive PCR approaches to quantitation of nucleic acid sequences overcome the limitations of basic PCR methods for quantitation. We have developed a competitive PCR method known as quantitative competitive PCR for quantitation of HIV DNA and RNA sequences. Key features of the technique include quantitation, based on the relative amounts of products produced from the target sequence and a competitive template introduced into test specimens, and stringent internal control of all reactions, including the reverse transcription step in RNA PCR. The method is suitable for analysis of clinical specimens and may be particularly valuable for accurate quantitation of viral load in patients undergoing treatment with experimental therapies.

Hepatitis E virus (HEV): strain variation in the nonstructural gene region encoding consensus motifs for an RNA-dependent RNA polymerase and an ATP/GTP binding site

Hepatitis is transmitted by a number of infectious agents. The epidemiological characterization of waterborne or enterically transmitted non-A, non-B hepatitis (ET-NANBH) is unique when compared with other known hepatitides. We have reported on the molecular cloning of a cDNA clone derived from the etiologic agent associated with ET-NANBH, the hepatitis E virus (HEV). The complete sequence of these first molecular clones, isolated from an HEV-infected human after passage in Macaca fascicularis (cynomolgus macaques), illustrates a distant relationship to other known positive-strand RNA viruses of plants and animals. The translated major open reading frame (ORF-1) from these clones indicates that this portion of the genome encodes a polyprotein with consensus sequences found in RNA-dependent RNA polymerase and ATP/GTP binding domains. The latter activity has been associated with putative helicases of positive-strand RNA viruses. These viral-encoded enzymatic activities identify this region and ORF-1 as containing at least two different nonstructural genes involved in HEV replication. Molecular clones obtained from two other geographically distinct HEV isolates demonstrated sequence heterogeneity in this nonstructural gene region. Further study will be required to elucidate the pathogenic significance (if any) of this observed divergence in the nonstructural region.

[A new blockout instrument for the construction of rotational path removable partial dentures. A case report]

This article introduces a new blockout device for rotational path removable partial dentures. The concept of rotation axis is discussed, from which a more convenient tool for clinical use is derived. The blockout instrument can be divided into three parts: the acrylic block, the rotation axis and the functional part. In the case of tilted mandibular molars, distal and lingual surfaces of anterior abutments should be blocked out according to the rotational path of insertion. In the blockout procedures, the blockout instrument is mounted between the two rotation centers on the two distal abutments with dental stone, so as to coincide the rotation axis of the instrument and that of the denture to be constructed. After the areas below the survey line of the anterior abutments are aproned with wax, Duralay resin is applied onto the areas above the survey line, and extended to join the functional parts of the blockout instrument. After setting, Duralay resin is removed and the portion above the survey line is trimmed to form a knife edge which corresponds to the survey line. Thereafter, the blockout areas are determined by the rotation movement of the knife-edge shaped Duralay resin along the rotation axis of the blockout instrument. This blockout method is more easily performed compared to the method mentioned by Firtell and Jacobson. In addition to the function of blockout, it can also be assisted in analyzing undercut and diagnosis.

Isolation of a cDNA from the virus responsible for enterically transmitted non-A, non-B hepatitis

Major epidemic outbreaks of viral hepatitis in underdeveloped countries result from a type of non-A, non-B hepatitis distinct from the parenterally transmitted form. The viral agent responsible for this form of epidemic, or enterically transmitted non-A, non-B hepatitis (ET-NANBH), has been serially transmitted in cynomolgus macaques (cynos) and has resulted in typical elevation in liver enzymes and the detection of characteristic virus-like particles (VLPs) in both feces and bile. Infectious bile was used for the construction of recombinant complementary DNA libraries. One clone, ET1.1, was exogenous to uninfected human and cyno genomic liver DNA, as well as to genomic DNA from infected cyno liver. ET1.1 did however, hybridize to an approximately 7.6-kilobase RNA species present only in infected cyno liver. The translated nucleic acid sequence of a portion of ET1.1 had a consensus amino acid motif consistent with an RNA-directed RNA polymerase; this enzyme is present in all positive strand RNA viruses. Furthermore, ET1.1 specifically identified similar sequences in complementary DNA prepared from infected human fecal samples collected from five geographically distinct ET-NANBH outbreaks. Therefore, ET1.1 represents a portion of the genome of the principal viral agent, to be named hepatitis E virus, which is responsible for epidemic outbreaks of ET-NANBH.

GLQ223: an inhibitor of human immunodeficiency virus replication in acutely and chronically infected cells of lymphocyte and mononuclear phagocyte lineage

GLQ223 is a highly purified, formulated preparation of trichosanthin, a 26-kDa plant-derived ribosome-inactivating protein with potent inhibitory activity against human immunodeficiency virus (HIV) in vitro. The compound produced concentration-dependent inhibition of HIV replication in acutely infected cultures of T-lymphoblastoid cells (VB cell line). Treatment with GLQ223 selectively reduced levels of detectable viral proteins compared to total cellular protein synthesis and produced a selective decrease in levels of viral RNA relative to total cellular RNA in acutely infected cells. Substantial inhibition of viral replication was observed at concentrations of GLQ223 that showed little inhibition of parallel uninfected cultures. Selective anti-HIV activity was also observed in cultures of primary monocyte/macrophages chronically infected with HIV in vitro. When freshly drawn blood samples from HIV-infected patients were treated with a single 3-hr exposure to GLQ223. HIV replication was blocked for at least 5 days in subsequently cultured monocyte/macrophages, without further treatment. The anti-HIV activity of GLQ223 in both acutely and chronically infected cells and its activity in cells of both lymphoid and mononuclear phagocytic lineage make it an interesting candidate as a potential therapeutic agent in HIV infection and AIDS.

Isolation of a chicken thioredoxin cDNA clone. Thioredoxin mRNA is differentially expressed in normal and Rous sarcoma virus-transformed chicken embryo fibroblasts

We have isolated a cDNA clone for chicken thioredoxin by differential screening of a cDNA library. The protein product which this clone encodes is very similar to other thioredoxins, and it displays thioredoxin activity when expressed in Escherichia coli. This clone represents the first metazoan thioredoxin for which the protein or nucleic acid sequence is known. Comparison of the chicken thioredoxin protein sequence with those from bacteria and plants indicates structural features that appear to be essential for activity. Transformation of chicken embryo fibroblasts by Rous sarcoma virus elevates the level of thioredoxin mRNA whereas the level of thioredoxin mRNA in a nonproliferative tissue (brain) is much lower than in chicken embryo fibroblasts.

Constitutive expression of a gene encoding a polypeptide homologous to biologically active human platelet protein in Rous sarcoma virus-transformed fibroblasts

A molecular clone corresponding to a 1.2-kilobase mRNA enriched in Rous sarcoma virus-transformed chicken embryo fibroblasts (CEF) was identified by differential screening of a cDNA library. The induction of the cloned sequence (denoted pCEF-4) in CEF infected by the temperature-sensitive mutant NY72-4 Rous sarcoma virus is rapid and independent of protein synthesis. DNA sequencing of the 1.2-kilobase insert of CEF-4 revealed an open reading frame that predicts an 11-kDa protein. The predicted pCEF-4 gene product is homologous to human connective tissue-activating peptide III (CTAP-III) and platelet factor 4 (PF-4). Serum stimulation of quiescent normal CEF results in a rapid but transient expression of pCEF-4 mRNA. Hence, pCEF-4 mRNA is expressed at the G0-G1 transition and during the first G1 phase of normal CEF reentering the cell cycle. The expression of pCEF-4 mRNA in Rous sarcoma virus-transformed CEF appears to be the result of transcriptional activation and stabilization of the transcript.

The spleen necrosis virus int gene product expressed in Escherichia coli has DNA binding activity and mediates att and U5-specific DNA multimer formation in vitro

To facilitate the in vitro study of the spleen necrosis virus (SNV) int gene product, we expressed the viral int locus in an Escherichia coli expression vector. Antiserum made against the protein produced in bacteria precipitated a 44-kDa polypeptide from virus-infected chicken embryo fibroblasts. This result is consistent with the expected size of the SNV int polypeptide. In a protein blotting assay, the expressed protein binds strongly to DNA and was able to complex nonspecifically with both single- and double-stranded DNAs containing or lacking viral sequences. However, under solution conditions favoring transient DNA unwinding, DNA binding was confined to supercoiled molecules containing either the SNV att sequence (the viral cis-acting region required for integration) or the U5 region of the long terminal repeat alone. Under these conditions of specific binding, multimeric DNA species were formed by apparent intermolecular interaction between protein-DNA complexes. These data indicate that retroviral integration may require local DNA unwinding at the att site for complex formation between the int gene product and DNA. This complex may be an intermediate in the viral DNA insertion process.

Isolation and identification of "diazepam-like" compounds from bovine urine

Attempts to isolate the putative endogenous ligand for the benzodiazepine receptor from bovine urine resulted in the identification of three isoflavans: equol (1), 3',7-dihydroxyisoflavan (2), and 4'-hydroxy-7-methoxyisoflavan (9), as "diazepam-like" compounds. 3-Chloro-9H-carbazole (17) was found to enhance the binding of diazepam in the benzodiazepine receptor binding assay. Pinosylvine monomethyl ether (18), indigo (20), and indirubin (21) were isolated as inactive compounds.

The tL2 cluster of transcription termination sites between genes bet and ral of coliphage lambda

The major leftward transcription of bacteriophage lambda is controlled by several terminators (t), including tL1, tL2, tL3, and others. The tL2 termination site, which was placed by Salstrom and Szybalski (Virology 88, 252-260, 1978) between lambda genes bet and ral, was found to consist of a cluster of four leftward terminators. As not to change the numbering of other leftward terminators, these were designated as tL2a, tL2b, tL2c, and tL2d. As determined by S1 nuclease mapping of the tL2-terminated in vitro transcripts, the normally pL-initiated major leftward lambda transcription should encounter termination points at 1653 bp (tL2a; between genes Ea10 and ral), 2089 bp (tL2b; between genes cIII and Ea10), 2441-2442 bp, and 2483 bp (tL2c and tL2d; both within gene gam) from the sL startpoint (= +1). All terminators were cloned in a pBR322-derived plasmid between the p'R promoter and the galK gene, and their in vivo termination efficiencies are 69% (tL2a), 53% (tL2b), and 38% (tL2c + tL2d), measured as reduction of galK expression in rho+galK- hosts at 30 degrees. The tL2a and tL2b), terminators depend little on the rho factor, whereas the efficiency of tL2c + tL2d decreases from 38 to only 14% in the rho- host. When shifted to 42 degrees, the termination efficiency of tL2b decreases from 53 to only 36%, while the other tL2 terminators are much less affected by increasing the temperature. The calculated joint efficiency of the entire tL2 cluster is 90%, which is in perfect agreement with the 90% termination efficiency reported by Salstrom and Szybalski (1978) for tL2. However, the natural location of tL2c and tL2d within the actively translated gam gene may interfere with their termination function. Under in vitro conditions, tL2c and tL2d are active only in the presence of rho factor, whereas tL2a and tL2b do not require rho. The structure of the tL2 terminators resembles that of some other known termination sites: a perfect (8 bp for tL2a and tL2b) or imperfect (8-9 bp) dyad symmetry and a T6 (tL2a), T5 (tL2b), T4 (tL2c) or TTATT sequence (tL2d) toward the 3' end of the mRNA-like DNA strand.

A cluster of leftward, rho-dependent t'J terminators in the J gene of coliphage lambda

While searching for the N-unresponsive terminator described by Honigman (Gene 13 (1981) 299-309), a 1680-bp DNA fragment from within gene J of bacteriophage lambda was cloned into plasmid pD12 between promoter p'R and the galK gene. In vitro transcription of this plasmid and S1 mapping assays, together with nucleotide sequencing, demonstrated that this DNA fragment contains a cluster of at least four in rho+ Escherichia coli hosts and only 30% in rho- hosts at at 30 degrees C. At the elevated temperature of 42 degrees C, the rho-dependent termination component of the t'J cluster becomes somewhat leaky, with the readthrough increasing by about twofold. The t'J terminators appear to be less responsive to nutR- and N-mediated antitermination (efficiency of 84-87%) than tL3, which responds to the same antitermination function with an efficiency of 97%. The relationship between the t'J cluster and the same antitermination function with an efficiency of 97%. The relationship between the t'J cluster and the highly N-unresponsive leftward termination signal tJ, which is also located within the J gene region (Gottesman et al., J. Mol. Biol. 140 (1980) 57-75; Honigman, Gene 13 (1981) 299-309), is unknown.

Tandem transcription-termination sites in the late rightward operon of bacteriophage lambda

A transcription termination site (designated as t'R2) is located between the rightward late t'R1 terminator and the S gene of phage lambda. This t'R2 terminator is rightward and absolutely dependent on the rho factor, being about 45% effective in rho+ E. coli and only 6% in rho- cells at 30 degrees C. This 7.5-fold rho dependence of t'R2 is in contrast to that of tR1 (4.5 fold, from about 81% to 18%) and the partial rho dependence of t'R1 (1.4 fold, from 96% to 67%). At the elevated temperature of 42 degrees C, t'R2 becomes 1.5 times more leaky (with about 2.5-fold reduction in termination efficiency) than tR1 or t'R1 (with only 1.1-fold reduction) in rho+ hosts. The calculated joint efficiencies of t'R1 and t'R2 are 98% in rho+ cells at 30 degrees C. t'R2 is also active in vitro, but only in the presence of rho factor, whereas t'R1 is active both in the presence and absence of rho. However, the in vitro termination at t'R1 is enhanced about 1.7-fold by the rho factor. The properly oriented lambda nutR site together with the N gene function bring about almost complete antitermination at t'R2 (96% effective), but incomplete at t'R1 (72%). The termination points at t'R2 are located around 532-534 bp to the right of the s'R startpoint of the p'R-initiated RNA on lambda DNA (or 338-340 bp downstream of t'R1) and 66-68 bp to the left of the S gene, as determined by S1 mapping. The t'R2 termination points are located within a dyad symmetry region which, in the transcript, is able to form a hairpin structure consisting of 16 bp in the stem and 6 bases in the loop. It is proposed that t'R2 acts as a second terminator to block any readthrough transcription initiated at the late promoter p'R into the late genes of phage lambda.

Effect of multiplicity of infection on transcription in Escherichia coli cells infected by bacteriophage lambda

The effect of multiplicity of infection (m.o.i.) on transcription was studied by infecting Escherichia coli with bacteriophage lambda cI47, lambda cI47O29P3 and lambda cI857cro27P3. DNA-RNA hybridization with lambda cI47 l-strand DNA, phi 80imm lambda r-strand DNA, and lambda imm80 r-strand DNA were used to measure mRNA transcription from the l-strand, the r-strand of the early x-P-Q region and the late A-J-b2 region of lambda bacteriophage respectively. In lambda cI47cro+O-P--infected cells, transcription from the l-strand, r-strand of the early x-P-Q region and the late A-J-b2 region all decreased with increasing m.o.i. The response in the x-P-Q region was less marked than in other regions, but the pattern looked similar to that described above. When phage DNA replication was permitted, as in the case of lambda cI47, the response was similar to that observed in lambda cI47cro+O-P--infected cells, but the level of transcription was increased two- or threefold. In lambda cI857cro-P--infected cells, the leftward transcription and the rightward transcription from the early x-P-Q region and the late A-J-b2 region all increased with increasing m.o.i., but the extent of change was less drastic than with lambda cro+. This result demonstrated clearly that the decrease in transcription from various regions at increasing m.o.i. of lambda cro+ was due to the inhibitory action of the cro gene product. The results obtained with cro- strongly support the view that gene dosage is a significant controlling factor for the extent of gene expression.

A rho-independent termination caused by the cloned inverted nut L site of phage lambda

For studying the termination activity of inverted nutL site of bacteriophage lambda, we have constructed a plasmid carrying the nutL fragment oriented reversely with respect to cloned lambda promoter p'R-directed transcription. The results of in vitro transcription on this plasmid template and S1 mapping assay reveal that the termination of p'R-promoted transcription at inverted nutL site is a rho-independent event. This nutL terminator shares several features with the other known sites of transcription termination, including (i) a uridine-rich 3' terminal RNA sequences,--UUAAUUUUU-OH, (ii) a GC-rich region in the DNA immediately preceding the site of termination, (iii) a region of dyad symmetry in the DNA which, in transcript, is capable of forming a stable hairpin containing four GC base pairs and one AU base pair in its stem.

Transcription termination: sequence and function of the rho-independent tL3 terminator in the major leftward operon of bacteriophage lambda

For cloning, assaying the function and sequencing terminators, we have constructed the pD12 plasmid, in which the late promotor p'R of phage lambda controls the expression of the galK gene of the pK03 plasmid of McKenney et al. (1981). The lambda tL3 terminator region was cloned in this plasmid between the promoter and the galK gene, and found to be 90-94% effective in preventing galactokinase expression in both rho+ and rho- hosts. Is is also active in vitro, both in the presence or absence of the rho factor. The termination point is located at 4320 bp to the left of the SL startpoint of the PL-RNA, just downstream of gene exo. We have sequenced 356 bp of the hitherto uncharted lambda DNA to the right of the TaqI cut, which in turn is 110 bp to the right of the b522 deletion at 63.9% lambda. The tL3 terminator has several features common to other rho-independent termination sequences, including an 81% G+C-rich region of 2X8-bp symmetry ("stem") with a 5-bp intervening "loop", partially overlapping and followed by a sequence transcribed into the pyrimidine-rich CCUUUCU-OH 3' terminus of the RNA. The termination point that follows the last U was determined by the S1 mapping technique.

Toxic effects of chromic sulphate on the common carp, Cyprinus carpio

The effects of chromic sulphate, which is commonly used in the tanning of leather, on the common carp, Cyprinus carpio and the bighead, Aristichthys nobilis, were studied. C. carpio was found to be more susceptible than A. nobilis to chromic sulphate at the lowest concentration tested (100 mg/l) whereas results obtained at other concentration were similar for both species. Damage to the gills, liver and intestine was observed by histopathological examination. A wide range of chemicals is used in the different stages of treating leather and a possible treatment of the effluent from the tanneries is suggested.

Gene dosage as a regulatory factor for gene expression. I. In lambda plac5-infected cells

To study the effect of gene dosage on gene expression, lambda plac5cI857O29P3, a replication defective lambda phage carrying part of the lac operon (containing the lac promotor, operator and z gene) in the b2 region was studied in Escherichia coli strain JC6256 where the lac operon is deleted and at a temperature where the lambda repressor is inactive. In measuring the synthesis of beta-galactosidase, it was possible to separate the effects of the lac promoter from those of the phage promoter. When the synthesis of beta-galactosidase was initiated from the inserted lac promoter in JC6256(lambda +) in the presence of additional cyclic AMP, the rate and level of beta-galactosidase synthesis were directly proportional to the multiplicity of infection (gene dosage). Furthermore, beta-galactosidase synthesis was initiated about 5 min after infection, just as with isopropyl-beta-D-thiogalactoside (IPTG) induction. When the synthesis of beta-galactosidase was initiated from the phage promoter in JC6256 in the absence of additional cyclic AMP, the rate and level of beta-galactosidase synthesis were again linearly proportional to gene dosage. On the other hand, initiation of beta-galactosidase synthesis was delayed until 10 to 20 min after infection. These results suggest that: (i) in the absence of negative controlling factors, the extent of gene expression is proportional to gene dosage; (ii) varying the gene dosage can be used to regulate gene expression.

The phage promoter responsible for the expression of the inserted beta-galactosidase gene in bacteriophage lambda plac5

The lac transducing phage, lambda plac5, carries a segment of the E. coli lac operon on the left side of the b2 region of the lambda phage. In the absence of additional cyclic AMP, beta-galactosidase can only be expressed from the phage promoter, and the expression of the inserted lac promoter is suppressed. This phage promoter responsible for beta-galactosidase synthesis is shown to be under the control of the cI and N gene products; however, the repressive action of the cro gene product at high multiplicity of infection is not observed although some turn off at very late time is detected. To pin down this phage promoter, results described in this communication and those described elsewhere can rule out the promoter PI, PR, P'R, and the promoter PL also looks rather unlikely. No firm identification of this phage promoter has been made, but the promoter(s) in the b2 region (the b2 promoter) is proposed. The phage promoter responsible for beta-galacrosidase synthesis is shown to be a weak promoter, requires the Q gene product or one (or more) of the late gene products for activation, and the time of expression is very late.