Hyperfine-field-mediated spin beating in electrostatically bound charge carrier pairs

Organic semiconductors offer a unique environment to probe the hyperfine coupling of electronic spins to a nuclear spin bath. We explore the interaction of spins in electron-hole pairs in the presence of inhomogeneous hyperfine fields by monitoring the modulation of the current through an organic light emitting diode under coherent spin-resonant excitation. At weak driving fields, only one of the two spins in the pair precesses. As the driving field exceeds the difference in local hyperfine field experienced by electron and hole, both spins precess, leading to pronounced spin beating in the transient Rabi flopping of the current. We use this effect to measure the magnitude and spatial variation in hyperfine field on the scale of single carrier pairs, as required for evaluating models of organic magnetoresistance, improving organic spintronics devices, and illuminating spin decoherence mechanisms.

Spin Rabi flopping in the photocurrent of a polymer light-emitting diode

Electron spin is fundamental in electrical and optical properties of organic electronic devices. Despite recent interest in spin mixing and spin transport in organic semiconductors, the actual spin coherence times in these materials have remained elusive. Measurements of spin coherence provide impartial insight into spin relaxation mechanisms, which is significant in view of recent models of spin-dependent transport and recombination involving high levels of spin mixing. We demonstrate coherent manipulation of spins in an organic light-emitting diode (OLED), using nanosecond pulsed electrically detected electron spin resonance to drive singlet-triplet spin Rabi oscillations. By measuring the change in photovoltaic response due to spin-dependent recombination, we demonstrate spin control of electronic transport and thus directly observe spin coherence over 0.5 s. This surprisingly slow spin dephasing underlines that spin mixing is not responsible for magnetoresistance in OLEDs. The long coherence times and the spin manipulation demonstrated are crucially important for expanding the impact of organic spintronics.

In vitro selection and characterization of human immunodeficiency virus type 1 resistant to Zidovudine and tenofovir

In this study, we undertook to generate HIV-1 resistance to PMPA by in vitro passage and to characterize the cross-resistance patterns and RT mutations in the generated resistant virus. The HIV-1 A102-resistant to AZT was serially passaged for 4 months in the presence of increasing concentrations of PMPA up to maximum of 40 microM on the fresh MT-2 cells. After 25 passages, HIV-1 developed decreased sensitivity to PMPA after long-term in vitro exposure. Selected HIV-1 mutants were characterized by decreased susceptibility to PMPA (4-fold). This decrease could be related to PMPA resistant caused by an amino acid change associated with a V148M substitution. From these results, additional studies will be needed to determine whether a similar mutation in HIV RT develops in patients receiving PMPA or its orally bioavailable prodrug, tenofovir dipivoxil fumarate.

Inhibition of UL54 and UL97 genes of human cytomegalovirus by RNA interference

Short interfering RNAs (siRNAs), namely siUL54-1 and siU54-2 targeting UL54 (DNA polymerase) gene, and siUL97-1 and siUL97-2 targeting UL97 (phosphotransferase) gene, were used to inhibit respective genes of Human cytomegalovirus (HCMV) and consequently the virus infection process in human foreskin fibroblast (HFF) cultures. The virus infection was monitored by cell morphology (CPE), levels of UL83 and IE86 mRNAs, and virus antigen. The results showed that siUL97-2 remarkably inhibited viral CPE while other siRNAs were less inhibitory. The siRNAs reduced the levels of UL83 mRNA but not that of IE86 mRNA; again, siUL97-2 was most inhibitory. Particularly, siUL97-2 reduced the UL83 mRNA level 14, 19, 203, and 37 times at 24, 48, 72, and 96 hrs post infection (p.i.), respectively. When tested for the effect on viral antigen by immunofluorescent assay (IFA), UL97-2 exerted a marked inhibition. These results demonstrate the effectiveness of siRNAs against experimental HCMV infection and indicate their therapeutic potential.

Expression of an artificial polypeptide with a repeated tripeptide glutamyl-tryptophanyl-lysine in Saccharomyces cerevisiae

AIMS

Artificial genes, which encode 48 or 64 repeats of a tripeptide, glutamyl-tryptophanyl-lysine have been cloned to the yeast expression vector pAM82 containing the PHO5 promoter and expressed in Saccharomyces cerevisiae AH22.

METHODS AND RESULTS

When the yeast cells harbouring recombinant plasmids pALTG6-2 and pALTG4-4 were derepressed in Burkholder minimal medium (Toh-e, A., Ueda, Y., Kakimoto, S.I. and Oshima, Y. (1973) Journal of Bacteriology113, 727-738) containing low phosphate (0.03 g l-1 KH2PO4 and 1.5 g l-1 KCl), the expression was the highest after 24 h induction and the artificial polypeptides were synthesized to about 10% (pALTG6-2) and 14% (pALTG4-4) of the total cell protein.

CONCLUSIONS

The artificial polypeptides produced in yeast were made to react with the rabbit antiserum against the polypeptide purified from Escherichia coli and found only in the pellet fraction of cell lysates, indicating the formation of inclusion body. Artificial polypeptide consisting of Glu-Trp-Lys may be useful as partial supplement in food and feeds.

SIGNIFICANCE AND IMPACT OF THE STUDY

The production of single cell enriched with homopolymers of an essential amino acid in yeast might be an important tool of supplementing cereal diets and feed grain rations and could be used as means for improvement of the amino acid profile of single cell protein and production of pharmaceutical peptides.

Hepatocyte-specific gene expression by baculovirus pseudotyped with vesicular stomatitis virus envelope glycoprotein

We have developed the recombinant baculovirus pseudotyped with vesicular stomatitis virus (VSV) G protein. The VSV-G gene was under the control of the polyhedrin promoter so that it was expressed at high levels in infected insect cells but not in mammalian cells. The presence of VSV-G protein in purified baculovirus preparations was confirmed by Western analysis. This recombinant baculovirus also carried human AFP (alpha-fetoprotein) promoter for hepatocyte-specific gene expression. After an in vitro infection by a recombinant baculovirus carrying the luciferase gene under the control of human AFP promoter/enhancer (BacG-AFP-Luc(+)), the luciferase gene was expressed in AFP-producing Huh7, Hep3B, and HepG2 cell lines, but not in AFP-nonproducing cell lines. BacG-AFP-Luc(+) transduced with human hepatoma cells in vitro at an efficiency about fivefold greater than the recombinant baculovirus lacking VSV-G (the virus Bac-AFP-Luc(+)). The utilization of the AFP promoter/enhancer in a baculovirus vector could provide benefits in gene therapy applications.

Increased glyceraldehyde-3-phosphate dehydrogenase gene expression in human cervical cancers

OBJECTIVE

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a classical glycolytic protein. A higher level of GAPDH mRNA was found in lung, pancreas, and prostate cancers, but in cervical carcinoma there have not been any reports about the level of GAPDH gene expression. So, we tried to investigate the GAPDH gene expression patterns in cervical carcinomas compared to normal cervical tissues, and the relationships between the expression levels of this gene and conventional clinicopathological parameters were evaluated.

MATERIALS AND METHODS

In this study, 25 normal exocervical tissues, 35 primary untreated cervical cancer tissues, 2 cervical cancer cell lines, and 2 post-nude-mouse-derived cervical cancer cell lines were subjected to Northern blot analyses for GAPDH gene expression.

RESULTS

Northern blot analyses revealed that the levels of GAPDH gene expression were elevated in 34 of 35 (97%) cervical carcinoma tissues and all of the 4 cervical cancer cell lines compared to normal cervical tissues. The levels of GAPDH gene expression were more prominent in rapidly proliferating cervical carcinoma cells. The levels of the GAPDH gene expressions in cervical cancer tissues were not associated with conventional clinicopathological parameters including clinical stage, histological type, and degree of differentiation.

CONCLUSION

These results suggest that increased GAPDH gene expression is characteristic of human cervical carcinomas and that rapidly proliferating carcinoma cells express more enhanced GAPDH gene. Future gene therapy using antisense oligodeoxynucleotide directed against GAPDH mRNA might be another therapeutic tool for human uterine cervical carcinoma.

Molecular biological characterization of enterovirus variant isolated from patients with aseptic meningitis

In Korea, there was a big outbreak of aseptic meningitis in 1993. Six clinical isolates of enterovirus were obtained from patients with aseptic meningitis and were identified as echovirus type 9 by serotyping with a pool of neutralizing antisera. For molecular characterization of the isolates, the nucleotide sequences of 5'-noncoding region (NCR), VP4, VP2, VP1, 2A and 2C regions of the isolates were compared with the corresponding regions of echovirus type 9 Hill and Barty strains. Unlike Hill strain, Barty strain contained a C-terminal extension to the capsid protein VP1 with an RGD (argnine-glycine-aspartic acid) motif. To determine whether similar structural features were present in our isolates, their nucleotide sequences including the VP1 region were analyzed. All isolates exhibited the VP1 extension with the RGD motif. We concluded the Korean isolates in the year of 1993 as the echovirus type 9 Barty strain although the isolates showed 15-20% nucleotide sequence differences in the several genomic regions.

Rapid subgrouping of nonpolio enterovirus associated with Aseptic Meningitis by RFLP (Restriction Fragment Length Polymorphism) assay

In Korea, there was a big outbreak of Aseptic Meningitis due to enterovirus infection in 1993. Since virus isolation and neutralizing tests are too laborious and time-consuming for the detection of enterovirus from clinical specimen, we have developed a new molecular identification method for rapid subgrouping of isolates from patients with aseptic meningitis. For the rapid subgrouping of isolates, RT-PCR (Reverse Transcription-Polymerase Chain Reaction) and RFLP (Restriction Fragment Length Polymorphism) assays were used. We have selected two oligonucleotide primers from the conserved 5'-UTR/VP2 and VP1 regions. A 652 bp (base pair) product was amplified from the 5'-UTR/VP2 region of reference viruses and the isolates. For the subgrouping of the isolates by RFLP assay, we have used 12 reference viruses (Echovirus, E6, E9, E11, E12, Coxsackievirus, CB1, CB3, CB4, CB5, Coxsackievirus, CA9, CA16, CA21, CA24), which are the common viral agents associated with aseptic meningitis. By using subgroup-specific restriction enzymes BsmAI, , HinP1I, and PleI, the isolates were classified into Echovirus subgroups. We have also shown that subgrouping of the isolates by RFLP assay based on the VP1 region is possible.

Defective HIV-1 provirus encoding a multitarget-ribozyme inhibits accumulation of spliced and unspliced HIV-1 mRNAs, reduces infectivity of viral progeny, and protects the cells from pathogenesis

A HeLa T4 cell line containing a defective human immunodeficiency virus type 1 (HIV-1) DNA (HD4) was isolated. After transactivation with Tat, the HD4 DNA was transcribed into a single 3.7-kb mRNA that encodes a chimeric CD4/Env protein and a multitarget-ribozyme directed against multiple sites within the gp120 coding region of HIV-1 RNA (Chen et al., 1992). Early steps in HIV infection such as entry, reverse transcription, and proviral DNA formation were not affected in HD4 cells, and HD4 was efficiently transactivated after either HIV-1 or HIV-2 infections. HIV-2, which lacks all of the HIV-1-specific ribozyme target sites, replicated to high levels in HD4 cells whereas HIV-1 replication was selectively inhibited. Despite a reduced accumulation of all HIV-1 transcripts, transactivation of HD4 was efficient. Surprisingly, the most abundant, multiply spliced mRNAs were reduced even though they lack all of the ribozyme target sites. These results strongly suggest that the ribozyme co-localizes with unspliced HIV-1 pre-mRNA and/or genomic HIV-1 RNA in the nucleus. Cleavage of these precursor RNAs explains the reduction of all spliced and unspliced HIV-1 RNAs. Cleavage of genomic RNA probably contributed to the three-fold reduction in the infectivity of viral progeny. Thus, the HD4 ribozyme RNA functioned as a ribozyme in the nucleus and as a mRNA for a chimeric CD4/Env protein in the cytoplasm. Its unusual large size for a ribozyme (3.7 kb) indicates that, in the future, other antiviral proteins, like negative transdominant mutant HIV-1 proteins, may also be encoded to increase its antiviral potential in a gene therapy approach.

GB virus C/hepatitis G virus infection among Korean patients with liver diseases and general population

GB virus C and hepatitis G virus (GBV-C/HGV) have been identified from the patients with acute or chronic liver diseases as possible agents of non-B, non-C hepatitis by two different groups, independently. To investigate whether GBV-C/HGV plays a role among Korean patients with liver diseases, GBV-C/HGV RNA were evaluated in 337 sera by the reverse transcription polymerase chain reaction (RT-PCR) using specific primers derived from 5'-noncoding region of GBV-C/HGV genome. GBV-C/HGV RNA was identified in 11/337 (3.3%). They consisted of 1/160 (0.6%) and 10/177 (3.3%) among the general population and patients with liver diseases, respectively (P < 0.01). Nucleotide sequences of all PCR amplicons were determined by the dideoxy chain termination method and analyzed by molecular evolutionary methods. The phylogenetic tree showed all sequences could be divided into three genotypes. These results indicate that: (1) GBV-C/HGV already exist in Korea; (2) GBV-C/HGV may play some role as an etiologic factor among the Korean patients with liver diseases; (3) GBV-C/HGV infection is rare among Korean general population; and (4) there are at least three different types of GBV-C/HGV in Korea.

Pleomorphic adenoma of the trachea--a case report

An unusual tracheal tumor was found in a 50 year old male who was admitted due to mild dyspnea on exertion. Simple chest X-ray showed an abnormal mass shadow in the trachea and computerized chest tomogram revealed a tumor in the mid 1/3 of the trachea obstructing 80% of the lumen. Through a right thoracotomy incision, resection of a 2.5 cm segment of the trachea with end-to-end anastomosis was done and microscopic findings showed many cystic spaces with myxomatous hyalinous stroma. It was diagnosed as a pleomorphic adenoma of the trachea.

Inducible and conditional inhibition of human immunodeficiency virus proviral expression by vesicular stomatitis virus matrix protein

Besides its role in viral assembly, the vesicular stomatitis virus (VSV) matrix (M) protein causes cytopathic effects such as cell rounding (D. Blondel, G. G. Harmison, and M. Schubert, J. Virol. 64:1716-1725, 1990). DNA cotransfection assays demonstrated that VSV M protein was able to inhibit the transcription of a reporter gene (B. L. Black and D. S. Lyles, J. Virol. 66:4058-4064, 1992). We have confirmed these observations by using cotransfections with an infectious clone of human immunodeficiency virus type 1 (HIV-1) and found that the amino-terminal 32 amino acids of M protein which are essential for viral assembly were not required for this inhibition. For the study of the potential role of M protein in the shutoff of transcription from chromosomal DNA, we have isolated stable HeLa T4 cell lines which encode either a wild-type or a temperature-sensitive (ts) VSV M gene under control of the HIV-1 long terminal repeat promoter. Transcription of the M mRNA was transactivated after HIV-1 infections. A cell line which encodes the wild-type M protein was nonpermissive for either HIV-1 or HIV-2. A cell line that encodes the ts M gene was transfected with the infectious HIV-1 DNA or was infected with HIV-1 or HIV-2. In all cases, at 32 degrees C, the permissive temperature for M protein, the cells were nonpermissive for HIV replication. At 40 degrees C, the ts M protein was nonfunctional and both HIV-1 and HIV-2 were able to replicate at high levels. A comparison of the amounts of proviral HIV-1 DNAs and HIV-1 mRNAs at 10 and 36 h after HIV-1 infection demonstrated that proviral insertion had not been prevented by M protein and that the block in HIV-1 replication was at the level of proviral expression. The severe reduction of HIV-1 proviral transcripts demonstrates that the VSV M protein alone can inhibit expression from chromosomal DNA. These results strongly support the hypothesis that the VSV M protein is involved in the shutoff of host cell transcription. M protein was able to attenuate HIV-1 infections and protect the cell population from HIV-1 pathogenesis. The temperature-dependent switch from a persistent to a lytic HIV-1 infection in the presence of ts M protein could be useful for studies of HIV-1 replication and pathogenesis.

Cloning and characterization of cDNA coding for a new allergen from the house dust mite, Dermatophagoides farinae

A cDNA clone encoding a new allergen from the Dermatophagoides farinae cDNA lambda gt11 library was isolated and sequenced. There was no amino acid sequence homology with other known allergens. The gene product, beta-galactosidase fusion protein, of the truncated cDNA on blot reacted with IgE in 13 of 43 sera from patients allergic to mites. The affinity-purified fusion protein had a potent ability to release histamine from washed blood cells of the mite-allergic patients. Human specific IgE eluted from the fusion protein band on blots recognized a 39-kD component on blots of a mite body extract.

Molecular cloning and sequencing of the epidermal cell differentiation inhibitor gene from Staphylococcus aureus

We recently purified to homogeneity a protein inhibiting differentiation of cultured keratinocytes from extracellular products of Staphylococcus aureus, and named it epidermal cell differentiation inhibitor (EDIN). In the present study, we isolated and sequenced the structural gene coding for EDIN from Staphylococcus aureus E-1 using oligonucleotide probes on the basis of the partial amino acid sequence of the purified EDIN. DNA sequencing of the cloned DNA revealed an open reading frame encoding 247 amino acids as a precursor of EDIN, which included an NH2-terminal signal sequence of 35 amino acid residues. Processing of this precursor produces a mature EDIN protein composed of 212 amino acids with a calculated Mr of 23,782. The EDIN shared 35% amino acid homology with the ADP-ribosyltransferase C3 of Clostridium botulinum. These results with biological properties of EDIN described previously indicate that EDIN is a novel protein.

An operon containing the genes for cholesterol oxidase and a cytochrome P-450-like protein from a Streptomyces sp

The nucleotide sequence of the promoter region of the gene for cholesterol oxidase (choA) from Streptomyces sp. strain SA-COO was determined. We found an open reading frame (choP) that is located between a potential promoter sequence and the structural gene for the ChoA protein. Deletion analysis showed that the promoter region for choP is essential for expression of the choA gene. Mappings of S1 nuclease and primer extension of transcripts generated in vivo suggested that the synthesis of mRNA starts at a site 41 bases upstream from the ATG initiation codon of the choP gene. By Northern (RNA) blot analysis of the transcripts, we found a 2.9-kilobase transcript that is identical in size to the total sequence of the choP and choA genes. These results suggest that the two genes, choP and choA, are transcribed polycistronically under the control of the promoter that is upstream from the structural gene for choP. The choP gene encodes a protein of 381 amino acids with a calculated Mr of 41,668. The nucleotide sequence of the choP gene has a high degree of similarity to the sequence of the genes for cytochrome P-450s from humans and Pseudomonas species. A region of homology with the cytochrome P-450s from various organisms was identified in the choP protein and may represent a region associated with a binding site for heme iron. Analysis of the CO difference spectrum of an extract of Streptomyces lividans cells that carry a plasmid which includes the choP gene revealed a unique peak, characteristic of cytochrome P-450, which is identical to that obtained with the parent strain.

Nucleolar organizer regions of lymphomas in Korea

Nucleolar organizer regions (NORs) are loops of DNA which occur in the nucleoli of cells and which possess ribosomal RNA (rRNA) genes. The numbers and/or configurations of NORs have been thought to be related to cellular activities. To assess the applicability of NORs associated protein (Ag-NORs) in the field of diagnostic histopathology, a silver staining was done in paraffin sections of malignant lymphomas, tonsils and reactive lymph nodes and the numbers of Ag-NORs in the nuclei of low-grade and those of high-grade lymphomas were compared. A significant difference was found between the numbers of Ag-NORs in the nuclei of low-grade lymphoma (a mean of 1.3 per nucleus) and those of high-grade lymphomas (a mean of 4.2 to 8.3 per nucleus). The Ag-NORs were often observed in nuclei in areas where nucleoli themselves were not visible in H&E stain. It is suggested that this method would be of great value in the field of tumor histopathology.

Acetylation of blasticidin S by its producing actinomycetes

A blasticidin S-producing actinomycetes, Streptoverticillium sp. JCM 4673 possesses an enzyme activity which acetylates the drug in the presence of acetyl coenzyme A. The modified drug was biologically inactive when tested against protein synthesis in vivo and in vitro. Production of the enzyme which acetylates blasticidin S increases with formation of the antibiotic during cell growth.

Isolation and properties of a puromycin acetyltransferase from puromycin-producing Streptomyces alboniger

Puromycin 2"-N-acetyltransferase was isolated from cell extracts of puromycin-producing Streptomyces alboniger KCC S-0309 by ammonium sulfate fractionation, heat treatment to eliminate contaminant proteins and chromatography on DEAE-Toyopearl 650S. After PAGE (polyacrylamide gel electrophoresis) of the final fraction, a single protein band corresponding to puromycin 2"-N-acetyltransferase was detected. The molecular weight of the enzyme determined by SDS-PAGE and Sephadex G-150 chromatography was about 21,000 and 85,000, respectively, suggesting that the enzyme consisted of four subunits. The isoelectric point and the optimum pH for reaction were 6.2 and 7.7, respectively. The Km values for puromycin and acetyl coenzyme A were 40 microM and 67 microM, respectively. The enzyme was thermostable up to 70 degrees C for 12 minutes. It was shown, by using an in vitro protein synthesizing system from a puromycin-susceptible organism S. flavotricini subsp. pseudochromogenes V-13-1, that the isolated puromycin 2"-N-acetyltransferase could protect polyphenylalanine synthesis from inhibition by puromycin.

Mechanism of self-protection in a puromycin-producing micro-organism

Puromycin is a potent inhibitor of bacterial protein synthesis, but puromycin-producing Streptomyces alboniger KCC S-0309 is tolerant to the antibiotic in vivo. Puromycin bound to both 30S and 50S ribosomal subunits from S. alboniger and inhibited polyuridylate-directed polyphenylalanine synthesis by the ribosomes. However, the organism possessed a novel puromycin-inactivating enzyme which acetylated the antibiotic at the 2''-NH2 group of the O-methyltyrosine moiety.