The multiubiquitin-chain-binding protein Mcb1 is a component of the 26S proteasome in Saccharomyces cerevisiae and plays a nonessential, substrate-specific role in protein turnover

The 26S proteasome is an essential proteolytic complex that is responsible for degrading proteins conjugated with ubiquitin. It has been proposed that the recognition of substrates by the 26S proteasome is mediated by a multiubiquitin-chain-binding protein that has previously been characterized in both plants and animals. In this study, we identified a Saccharomyces cerevisiae homolog of this protein, designated Mcb1. Mcb1 copurified with the 26S proteasome in both conventional and nickel chelate chromatography. In addition, a significant fraction of Mcb1 in cell extracts was present in a low-molecular-mass form free of the 26S complex. Recombinant Mcb1 protein bound multiubiquitin chains in vitro and, like its plant and animal counterparts, exhibited a binding preference for longer chains. Surprisingly, (delta)mcb1 deletion mutants were viable, grew at near-wild-type rates, degraded the bulk of short-lived proteins normally, and were not sensitive to UV radiation or heat stress. These data indicate that Mcb1 is not an essential component of the ubiquitin-proteasome pathway in S.cerevisiae. However, the (delta)mcb1 mutant exhibited a modest sensitivity to amino acid analogs and had increased steady-state levels of ubiquitin-protein conjugates. Whereas the N-end rule substrate, Arg-beta-galactosidase, was degraded at the wild-type rate in the (delta)mcb1 strain, the ubiquitin fusion degradation pathway substrate, ubiquitin-Pro-beta-galactosidase, was markedly stabilized. Collectively, these data suggest that Mcb1 is not the sole factor involved in ubiquitin recognition by the 26S proteasome and that Mcb1 may interact with only a subset of ubiquitinated substrates.

The incidence of insulin-dependent diabetes mellitus in urban districts of Shanghai (1989-1993)

A retrospective study on the incidence of insulin-dependent diabetes mellitus (IDDM) among children aged 0-14 years was carried out from 1989-1993 in urban Shanghai, China. The average annual population at risk (0-14 yr) consisted of 1,401,664 children. All the cases were collected from the hospitals (primary source) and from primary and middle schools and kindergartens (second source) with independent validation of case ascertainment. There were 53 IDDM cases from the primary source, 23 from the secondary source, with a total of 58. The ascertainment corrected total number of IDDM cases was 67 by the capture-recapture method. The average crude annual incidence rate was 0.83 [95% confidence interval (CI) 0.61-1.04] and ascertainment corrected incidence rate 0.96 (95% CI 0.80-1.12) per 100,000. Peak incidence fell in 1992 and in the 9 year-old group. The incidence of childhood IDDM in the urban districts of Shanghai was reconfirmed to be the lowest in the world but by comparing the results of former investigations a trend was found of increasing incidence of IDDM.

Phage display vectors for in vivo recombination of immunoglobulin heavy and light chain genes to make large combinatorial libraries

New phage display vectors for in vivo recombination of immunoglobulin (Ig) heavy (VH) and light (VL) chain variable genes, to make single-chain Fv fragments (scFv), were constructed. The VH and VL genes of monoclonal antibody (mAb) EP-5C7, which binds to both human E- and P-selectin, were cloned into a pUC19-derived plasmid vector, pCW93, and a pACYC184-derived phagemid vector, pCW99, respectively. Upon induction of Cre recombinase (phage P1 recombinase), the VH and VL genes were efficiently recombined into the same plasmid via the two loxP sites (phage P1 recombination sites), one located downstream from a VH gene in pCW93 and another upstream from a VL gene in pCW99. In the resulting phagemid, the loxP sequence also encodes a polypeptide linker connecting the VH and VL domains to form a scFv of EP-5C7. Whether expressed on the phage surface or as a soluble form, the EP-5C7 scFv showed specific binding to human E- and P-selectin. This phagemid vector system provides a way to recombine VH and VL gene libraries efficiently in vivo to make extremely large Ig combinatorial libraries.

Cancer mortality among shoe manufacturing workers: an analysis of two cohorts

OBJECTIVES

To examine the cancer risk of shoe manufacturing workers and evaluate whether the risk was associated with exposure to leather dust and solvents.

METHODS

Data from two historical cohort studies of shoe workers were expanded and analysed in parallel. A total of 4215 shoemakers from England contributing 103 726 person-years at risk and 2008 shoemakers from Florence, Italy, contributing 54,395 person-years at risk were included in the analysis. Exposure to leather dusts and solvents from glues was evaluated on the basis of job title information. Standardised mortality ratios (SMR) were calculated as ratios of observed deaths (Obs) over expected derived from national mortalities.

RESULTS

Overall mortality was lower than expected in both cohorts (English cohort: Obs 3314, SMR 81, 95% confidence interval (95% CI) 78-84; Florence cohort: Obs 333, SMR 87, 95% CI 78-97). An increased risk of nasal cancer was found (English cohort: Obs 12, SMR 741; Florence cohort: Obs 1, SMR 909). 10 of the 13 cases occurred among English workers employed in the manufacture of welted boots (SMR 926, 95% CI 444-1703), a sector of the industry thought to have had the highest exposure to leather dust. Mortality from leukaemia was not increased in the English cohort (Obs 16, SMR 89), but was increased in the Florence cohort (Obs 8, SMR 214, 95% CI 92-421); and the highest risk was found among shoe workers in Florence who were first exposed between 1950 and 1959 when exposure to benzene was substantial (Obs 3, SMR 536, 95% CI 111-1566). Some evidence for an excess risk of stomach, bladder, and kidney cancer, as well as multiple myeloma and non-Hodgkin's lymphoma was also found in the Florence cohort only among workers employed in jobs with the highest exposure to solvents.

CONCLUSIONS

These findings confirm the associations between exposure to leather dust and nasal cancer and between exposure to benzene and leukaemia in the shoe manufacturing industry and suggest that the risk of other cancers may be increased among workers exposed to solvents or glues.

Engineered biosynthesis of novel polyketides: regiospecific methylation of an unnatural substrate by the tcmO O-methyltransferase

TcmO is an O-methyltransferase that methylates the C-8 hydroxyl to Tcm B3, a four-ring aromatic intermediate in the tetracenomycin biosynthetic pathway of Streptomyces glaucescens. The gene encoding this enzyme was expressed in Streptomyces coelicolor CH999 together with the actinorhodin polyketide synthase (PKS) gene cluster, which is responsible for the biosynthesis of 3,8-dihydroxy-methylanthraquinone carboxylic acid (DMAC) and its decarboxylated analog, aloesaponarin. The resulting recombinant strain produced approximately equal quantities of aloesaponarin and a new product but no DMAC. Spectroscopic analysis revealed that the novel polyketide was the 3-O-methylated analog of DMAC. An in vitro radioisotopic assay was developed for tcmO. The enzyme requires S-adenosylmethionine as a co-substrate. It has a Km of 3 microM and a kcat of 2.7 min-1 for DMAC. A series of monocyclic, bicyclic, and tricyclic aromatic compounds were also tested as candidate substrates in vitro. Remarkably, none was modified by tcmO within detectable limits of the assay. Together, these results highlight the interesting molecular recognition features of this enzyme. On one hand, there appears to be some flexibility in the number and structures of unreactive rings, since both Tcm and B3 and DMAC are good substrates. However, 6-methylsalicylic acid, a monocyclic analog of the reactive ring, is not recognized by the enzyme. Likewise, neither aloesaponarin (which only differs from DMAC in the reactive ring) nor carminic acid (which only differs in the distal nonreactive ring) is modified. Thus, the binding energy for the tcmO-catalyzed methyl transfer appears to involve significant contributions from both the aromaticity and the functionality of polycyclic substrates.

Enhanced infectivity of modified bluetongue virus particles for two insect cell lines and for two Culicoides vector species

Previous studies (Mertens et al., Virology 157, 375-386, 1987) have shown that removal of the outer capsid layer from bluetongue virus (BTV) significantly reduces (approximately x 10(-4)) the infectivity of the resultant core particle for mammalian cells (BHK 21 cells). In contrast, the studies reported here, using a cell line (KC cells) derived from a species of Culicoides that can act as a vector for BTV (Culicoides variipennis), demonstrated a much higher infectivity of core particles than that in mammalian cells (approximately x 10(3)). This increase resulted in a specific infectivity for cores that was only 20-fold less than that of purified disaggregated virus particles (stored in the presence of 0.1% sodium-N-lauroylsarcosine (NLS)). Removal of this detergent caused intact virus particle aggregation and (as previously reported) resulted in an approximately 1 log10 drop in the specific infectivity of those virus particles which remained in suspension. In consequence the specific infectivity of core particles for the KC cells was directly comparable to that of the intact but aggregated virus. These data are compared with the results from oral infectivity studies using two vector species (C. variipennis and Culicoides nubeculosus), which showed similar infection rates at comparable concentrations of purified cores, or of the intact but aggregated virus particles (NLS was toxic to adult flies). The role of the outer core proteins (VP7) in cell attachment and penetration, as an alternative route of initiation of infection, is discussed. Previous studies (Mertens et al., Virology 157, 375-386, 1987) also showed that the outer capsid layer of BTV can be modified by proteases (including trypsin or chymotrypsin), thereby generating infectious subviral particles (ISVP). The specific infectivity of ISVP for mammalian cells (BHK21 cells) was shown to be similar to that of disaggregated virus particles. In contrast, we report a significantly higher specific infectivity of ISVP but not of the intact virus (approximately x 100) for two insect cell lines (KC cells and C6/36 mosquito cells (derived from Aedes albopictus)). In oral infection studies with adults of the two vector species, ISVP produced the same infection rate at approximately 100-fold lower concentrations than either core particles or the intact but aggregated virus particles. The importance of mammalian host serum proteases, or insect gut proteases, in modification of the intact virus particle to form ISVP and their role in initiation of infection and the vector status of the insect is discussed.

Engineered biosynthesis of novel polyketides: properties of the whiE aromatase/cyclase

The ORFVI from the cluster of genes, which is responsible for the biosynthesis of the Streptomyces coelicolor spore pigment, the whiE cluster, has been described as a bifunctional aromatase/cyclase. In order to evaluate its potential use for generating novel polyketides, combinations of this gene with those encoding minimal polyketide synthase enzymes with or without a ketoreductase from S. coelicolor A3(2) were constructed and analyzed in vivo. Analysis of the polyketide products generated from these constructs indicates that the whiE-ORFVI enzyme has properties similar to those of TcmN, although the whiE aromatase/cyclase normally acts on a polyketide intermediate that is four carbons longer than the TcmN substrate. The whiE aromatase/cyclase can influence the regiospecificity of the first cyclization of unreduced, but not reduced, backbones and is also responsible for the second ring aromatization. An unusual new polyketide, EM18, was identified which is not seen in equivalent strains expressing the tcmN aromatase/cyclase or the act aromatase genes. The structure of EM18 suggests that the WhiE-ORFVI product might have some unique properties within this family of polyketide synthase subunits, and may therefore be useful in the design of combinatorial biosynthetic strategies.

Deciphering the biosynthetic origin of the aglycone of the aureolic acid group of anti-tumor agents

BACKGROUND

Mithramycin, chromomycin, and olivomycin belong to the aureolic acid family of clinically important anti-tumor agents. These natural products share a common aromatic aglycone. Although isotope labeling studies have firmly established the polyketide origin of this aglycone, they do not distinguish between alternative biosynthetic models in which the aglycone is derived from one, two or three distinct polyketide moieties. We set out to determine the biosynthetic origin of this moiety using a recombinant approach in which the ketosynthase and chain-length factor proteins from the antibiotic-producer strain, which determine the chain length of a polyketide, are produced in a heterologous bacterial host.

RESULTS

The ketosynthase and chain-length factor genes from the polyketide synthase gene cluster from the mithramycin producer, Streptomyces argillaceus ATCC 12956, and the acyl carrier protein and ketoreductase genes from the actinorhodin polyketide synthase were expressed in Streptomyces coelicolor CH999. The recombinant strain produced a 20-carbon polyketide, comprising the complete backbone of the aglycone of mithramycin.

CONCLUSIONS

The aglycone moieties of mithramycin, chromomycin, and olivomycin are derived from a single polyketide backbone. The nascent polyketide backbone must undergo a series of regiospecific cyclizations to form a tetracenomycin-like tetracyclic intermediate. The final steps in the aglycone biosynthetic pathway presumably involve decarboxylation and oxidative cleavage between C-18 and C-19, followed by additional oxidation, reduction, and methylation reactions.

Antibiotic activity of polyketide products derived from combinatorial biosynthesis: implications for directed evolution

A library of over 100 polyketides, generated via combinatorial cloning of genes encoding subunits of aromatic polyketide synthases, was screened for molecules capable of inhibiting the growth of gram-positive bacteria. A total of 26 polyketides, with varying levels of antibiotic activity in filter-disk assays, were purified. Most bioactive polyketides were produced as relatively minor compounds (< 1 mg/l), although two major anthraquinones, with yields in the range of 10-100 mg/l, were also identified and structurally characterized. When tested against Bacillus subtilis 168 beta, they were found to cause a 50% reduction in colony-forming units at concentrations of 20 and 300 micrograms/ml, respectively. We speculate that many of the minor (and possibly more potent) bioactive polyketides are synthesized via nonspecific enzymatic modifications of shunt products derived from engineered polyketide synthase pathways. If so, then these 'fortuitous' pathways should be amenable to further rationally guided manipulation. Our results support the notion that combinatorial biosynthesis can be used to generate novel, biologically active molecules. They also point to the feasibility of designing mutagenesis selection experiments aimed at the directed evolution of organic molecules with desirable pharmaceutical properties.

[Survival rates in patients with systemic lupus erythematosus]

To assess the impact of demographic and clinical factors on prognosis in patients with systemic lupus erythematosus (SLE), we examined the survival rate by lifetable analysis in 566 patients. All patients were Shanghai citizens who were diagnosed as having SLE in Huashan Hospital between 1959 and 1992. According to American Rheumatism Association's preliminary criteria. The survival rate from the time of SLE onset was 93% at 1 year, 73% at 5 years and 60% at 10 years. On univariate analysis, we found that the following factors worsened the probability of survival; male, neuropsychiatric manifestation, pleurisy-pericarditis, anemia, thrombocytopenia, lymphocytopenia, proteinuria, hematuria, urinary cast, azotemia, decreased endogenous creatinine clearance, increased cholesterol in serum, hypocomplementemia, abnormal electrocardiograph and high corticosteroid dose of treatment. On multivariate analysis, we found the four independent risk factors were male, azotemia, hypocomplementemia and high corticosteroid dose of treatment.

Sink- and vascular-associated sucrose synthase functions are encoded by different gene classes in potato

Two differentially regulated classes of sucrose synthase genes, Sus3 and Sus4, were identified in potato. They cannot be classified as Sus1 and Sus2 types based on sequence homology and appear to have evolved after the divergence of the major families of dicotyledonous plants but before the divergence of tomato and potato. The potato sucrose synthase clones Sus3-65 and Sus4-16 share an 87% nucleotide identity in the coding regions, and both are interrupted by 13 introns, including a long leader intron. Potato Sus3 genes are expressed at the highest levels in stems and roots and appear to provide the vascular function of sucrose synthase. In contrast, Sus4 genes are expressed primarily in the storage and vascular tissue of tubers and appear to facilitate sink function. The genes are differentially regulated in root tips, with Sus3 expressed at high levels in the cell division zone and Sus4 expressed at high levels in the meristem and cap.

High-level tuber expression and sucrose inducibility of a potato Sus4 sucrose synthase gene require 5' and 3' flanking sequences and the leader intron

The 3.6 kb of 5' flanking sequence, leader intron, and 0.7 kb of 3' sequence from the potato sucrose synthase gene Sus4-16 are sufficient to direct high-level expression in developing tubers, in basal tissues of axillary buds and shoots, and in meristems and caps of roots, and to confer sucrose inducibility in leaves. By examining a series of deletion and substitution constructs in transgenic potato plants, we found that this pattern of expression requires 5' flanking sequences both upstream and downstream of position -1500 and that sequences between positions -1500 and -267 are essential for sucrose induction. Replacement of the native 3' sequence with the nopaline synthase 3' sequence resulted in the loss of sucrose inducibility and of expression in basal tissues of axillary buds. A general decrease in expression in other tissues was also observed. Removal of the 1612-bp leader intron also had a dramatic effect on both the pattern and level of expression.

High-level tuber expression and sucrose inducibility of a potato Sus4 sucrose synthase gene require 5' and 3' flanking sequences and the leader intron

The 3.6 kb of 5' flanking sequence, leader intron, and 0.7 kb of 3' sequence from the potato sucrose synthase gene Sus4-16 are sufficient to direct high-level expression in developing tubers, in basal tissues of axillary buds and shoots, and in meristems and caps of roots, and to confer sucrose inducibility in leaves. By examining a series of deletion and substitution constructs in transgenic potato plants, we found that this pattern of expression requires 5' flanking sequences both upstream and downstream of position -1500 and that sequences between positions -1500 and -267 are essential for sucrose induction. Replacement of the native 3' sequence with the nopaline synthase 3' sequence resulted in the loss of sucrose inducibility and of expression in basal tissues of axillary buds. A general decrease in expression in other tissues was also observed. Removal of the 1612-bp leader intron also had a dramatic effect on both the pattern and level of expression.

Sink- and vascular-associated sucrose synthase functions are encoded by different gene classes in potato

Two differentially regulated classes of sucrose synthase genes, Sus3 and Sus4, were identified in potato. They cannot be classified as Sus1 and Sus2 types based on sequence homology and appear to have evolved after the divergence of the major families of dicotyledonous plants but before the divergence of tomato and potato. The potato sucrose synthase clones Sus3-65 and Sus4-16 share an 87% nucleotide identity in the coding regions, and both are interrupted by 13 introns, including a long leader intron. Potato Sus3 genes are expressed at the highest levels in stems and roots and appear to provide the vascular function of sucrose synthase. In contrast, Sus4 genes are expressed primarily in the storage and vascular tissue of tubers and appear to facilitate sink function. The genes are differentially regulated in root tips, with Sus3 expressed at high levels in the cell division zone and Sus4 expressed at high levels in the meristem and cap.

A potato Sus3 sucrose synthase gene contains a context-dependent 3' element and a leader intron with both positive and negative tissue-specific effects

To examine which sequences are involved in regulating the potato sucrose synthase gene Sus3-65, we examined a series of deletion and substitution constructs in transgenic potato and tobacco plants. In a construct containing 3.9 kb of 5' flanking region, substitution of the native 3' sequence with the nopaline synthase 3' sequence and deletion of the leader intron did not significantly affect expression in vegetative tissues. However, in a construct containing only 320 bp of 5' flanking region, these changes had marked effects. Replacing the native 3' sequences with nopaline synthase 3' sequences caused a six- to 20-fold increase in expression in vascular tissue, and removing the leader intron almost completely abolished expression in potato plants. Surprisingly, removal of the leader intron from either the full-length construct or a construct containing only 320 bp of 5' flanking sequence reduced expression in vascular tissue of tobacco anthers at later stages of development but increased expression in pollen by more than 100-fold.

Crystal structure of the zeta isoform of the 14-3-3 protein

The 14-3-3 family of proteins have recently been identified as regulatory elements in intracellular signalling pathways: 14-3-3 proteins bind to oncogene and proto-oncogene products, including c-Raf-1 (refs 2-5), c-Bcr (ref. 6) and polyomavirus middle-T antigen; overexpression of 14-3-3 activates Raf kinase in yeast and induces meiotic maturation in Xenopus oocytes. Here we report the crystal structure of the major isoform of mammalian 14-3-3 proteins at 2.9 A resolution. Each subunit of the dimeric protein consists of a bundle of nine antiparallel helices that form a palisade around an amphipathic groove. The groove is large enough to accommodate a tenth helix, and we propose that binding to an amphipathic helix represents a general mechanism for the interaction of 14-3-3 with diverse cellular proteins. The residues in the dimer interface and the putative ligand-binding surface are invariant among vertebrates, yeast and plants, suggesting a conservation of structure and function throughout the 14-3-3 family.

Binding characteristics of glucocorticoid receptor in synaptic plasma membrane from rat brain

The study was carried out to identify the specific glucocorticoid membrane binding site (GCMB) on synaptic plasma membrane (SPM), and to investigate the ligand binding properties and physico-chemical characteristics of GCMB. The radioligand binding assay showed that tritiated corticosterone ([3H]B) could bind to GCMB specifically with positive cooperativity. For SPM, the binding capacity (R(zero)) was 46.67 +/- 4.62 fmol/mg protein; the dissociation constant (Kd), 97.48 +/- 18.85 nmol/L, and the Hill coefficient, 1.633 +/- 0.082. Various steroids bound with GCMB in the following rank order: RU26752, aldosterone > corticosterone, cortisol > RU26988, progesterone, R5020, triamcinolone acetonide > testosterone, estradiol > RU38486 > dexamethasone. GCMB, which could be solubilized by detergent Triton X-100, showed thermal stability, although it was susceptible to hydrolysis by trypsin and to the reducing agent, mercaptoethanol. The addition of divalent cations (Ca2+, Mg2+) was beneficial to the ligand binding. The results strongly indicate that GCMB, fulfilling the basic criteria for a receptor, constitutes a novel type of glucocorticoid receptor on neuronal membrane which is significantly different from the cytosolic glucocorticoid receptors.

Cancer and occupational exposure to inorganic lead compounds: a meta-analysis of published data

OBJECTIVES

To review and summarise the epidemiological evidence on the carcinogenicity of occupational exposure to inorganic lead.

METHODS

Case-control and cohort studies were reviewed and combined for meta-analysis. Fixed and random effect methods were used to estimate the summary effects.

RESULTS

The combined results show a significant excess risk of overall cancer, stomach cancer, lung cancer, and bladder cancer, with relative risk ratios (RRs) and 95% confidence intervals (95% CIs) in the meta-analysis of 1.11 (1.05-1.17), 1.33 (1.18-1.49), 1.29 (1.10-1.50), and 1.41 (1.16-1.71) respectively. The RR (95% CI) for kidney cancer was also high, but did not reach significance (1.19 (0.96-1.48)). A separate analysis of studies of heavily exposed workers provided slightly increased RRs for cancers of the stomach (1.50) and lung (1.42).

CONCLUSIONS

The findings from the workers with heavy exposure to lead provided some evidence to support the hypothesis of an association between stomach and lung cancer and exposure to lead. The main limitation of the present analysis is that the excess risks do not take account of potential confounders, because little information was available for other occupational exposures, smoking, and dietary habits. To some extent, the risk of lung cancer might be explained by confounders such as tobacco smoking and exposure to other occupational carcinogens. The excess risk of stomach cancer may also be explained, at least in part, by non-occupational factors. For bladder and kidney cancers, the excess risks are only suggestive of a true effect because of possible publication bias.

Retroreflecting ellipsometer for measuring the birefringence of optical disk substrates

A retroreflecting ellipsometer has been constructed for measuring the birefringence of optical disk substrates. In contrast to conventional ellipsometers with two mechanical arms, this system has only one arm along which both the incident and reflected beams travel. This construction eliminates the mechanical limitations of conventional ellipsometers, thereby permitting normal incidence on the sample. In addition, the single arm is adjustable in two dimensions, with the polar incident angle, θ(inc), varying from 0° to 70°, and the azimuthal incident angle, Φ(inc), varying from 0° to 360°. The condition of normal incidence permits accurate measurement of in-plane birefringence. The adjustability of both θ(inc) and Φ(inc) is necessary for the measurement of possible tilts of the index ellipsoid, and also for the variation of birefringence through the substrate thickness. Measurement results showing the useful features of the equipment are presented. The optics of the hemispherical assembly used for retroreflection as well as for the elimination of undesirable refractions are also studied by use of the ZEMAX lens design program.

Engineered biosynthesis of novel polyketides: evidence for temporal, but not regiospecific, control of cyclization of an aromatic polyketide precursor

BACKGROUND

Aromatic polyketide synthases (PKSs) catalyze the formation and cyclization of polyketide chains of variable lengths, generating a family of compounds of proven medical significance. Initial control over the regiospecificity of cyclization is believed to be exercised by the minimal PKS, composed of the three essential components for polyketide biosynthesis, which catalyzes an intramolecular aldol condensation towards the middle of the chain. Subsequent cyclization reactions are either catalyzed by additional components of the PKS, or occur in the absence of specific catalysts.

RESULTS

Structural and biosynthetic studies on SEK4b, a novel octaketide product of a minimal PKS, revealed an unusual cyclization pattern. The first cyclization (an aldol condensation) occurs at the methyl end of the unreduced polyketide backbone precursor. This is followed by hemiketal formation and lactonization. The overall structure of SEK4b is similar to that of SEK4, a previously-identified product of the same genetically-engineered strain, differing only in the positions of a methyl and a pyrone group around a common fused-ring system. The biosynthetic pathways of the two molecules are quite different, however. The yield of SEK4b relative to SEK4 is much higher in the absence of PKS components (aromatases and cyclases) acting later in the pathway.

CONCLUSIONS

In this cyclization pathway, the regiospecificity of cyclization is not directly controlled by the minimal PKS. Instead, we propose that the enzyme influences cyclization by controlling the timing of chain release. Chain release and cyclization may be concurrent with synthesis. Other PKS subunits appear to stabilize the complex of the PKS with the nascent chain, preventing premature release.

Engineered biosynthesis of novel polyketides: influence of a downstream enzyme on the catalytic specificity of a minimal aromatic polyketide synthase

To identify the minimum set of polyketide synthase (PKS) components required for in vivo biosynthesis of aromatic polyketides, combinations of genes encoding subunits of three different aromatic PKSs--act from Streptomyces coelicolor A3(2) (an actinorhodin producer), fren from Streptomyces roseofulvus (a frenolicin and nanaomycin producer), and tcm from Streptomyces glaucescens (a tetracenomycin producer)--were expressed in a recently developed Streptomyces host-vector system. The "minimal" components (ketosynthase/putative acyltransferase, chain length-determining factor, and acyl carrier protein) were produced with and without a functional polyketide ketoreductase and/or cyclase, and the polyketide products of these recombinant strains were structurally characterized. Several previously identified polyketides were isolated in addition to two previously unidentified polyketides, dehydromutactin and SEK 15b, described here. The results proved that the act cyclase is not required for the biosynthesis of several aberrantly cyclized products that have been previously reported. They are also consistent with earlier conclusions that the minimal PKS controls chain length as well as the regiospecificity of the first cyclization and that it can do so in the absence of both a ketoreductase and a cyclase. However, the ability of the minimal tcm PKS to synthesize two different singly cyclized intermediates suggests that it is unable to accurately control the course of this reaction by itself. In the presence of a downstream enzyme, the flux through one branch of the cyclization pathway increases relative to the other. We propose that these alternative specificities may be due to the ability of downstream enzymes to associate with the minimal PKS and to selectively inhibit a particular branch of the cyclization pathway.

A NaCl-regulated plant gene encoding a brain protein homology that activates ADP ribosyltransferase and inhibits protein kinase C

A cDNA clone pCZ1, with a 1.1 kb insert, was isolated from a NaCl-adapted tobacco cell cDNA library that encodes an apparently full-length 29 kDa protein (251 amino acids) with a calculated pI of 5.7. The encoded peptide had a high amino acid sequence identity with bovine 14-3-3 protein which was originally found as an abundant protein in the animal central nervous system. Recently, proteins with sequence identity to 14-3-3 protein have also been found in plants, insects and yeast, and appear to have diverse physiological functions. Similar to the bovine brain 14-3-3 protein, the recombinant pCZ1 protein stimulated ADP-ribosylation of protein substrate by ADP-ribosyltransferase from the plant and animal pathogenic bacterium Pseudomonas aeruginosa. This recombinant protein also inhibited protein kinase C activity in vitro. Southern blot analyses indicated that most likely five genes encoding 14-3-3-like proteins are present in tobacco. The pCZ1 cDNA insert hybridized to a single mRNA of 1.1 kb from cultured tobacco cells. The level of this mRNA transcript in tobacco cells was downregulated upon adaptation to NaCl but was unaffected by short-term treatment with NaCl, ABA or ethylene. In tobacco plants, expression of transcript that hybridized to pCZ1 was tissue specific, and was most abundant in roots and flower parts. Monoclonal antibody raised against GF14 protein, a maize protein with substantial sequence identity with 14-3-3 protein detected two bands on SDS-PAGE of total proteins from unadapted tobacco cells and only a single band from cells adapted to NaCl. The GF14 antibody was also used to illustrate that the G-box element of a salt-induced gene is associated with a 14-3-3-type protein.

Measurement of the wavelength dependence of birefringence for optical disk substrates

The in-plane and vertical birefringence of polycarbonate plastic substrates of optical disks are measured for wavelengths between 360 and 860 nm, which covers the full range of interest for blue as well as for the current red and infrared recording. It is found that the birefringence generally decreases as the measurement wavelength is increased. In a typical case, the in-plane birefringence, Δn‖ goes from 1.7 × 10(-5) to 1.2 × 10(-5), and the vertical birefringence, Δn⊥, drops from 7.5 δ 10(4-) to 5.7 × 10(4-) in the wavelength range from 360 to 860 nm.

Association of the protein kinases c-Bcr and Bcr-Abl with proteins of the 14-3-3 family

In this study, a protein that interacts with sequences encoded by the first exon of the protein kinase Bcr was cloned. The Bcr-associated protein 1 (Bap-1) is a member of the 14-3-3 family of proteins. Bap-1 interacts with full-length c-Bcr and with the chimeric Bcr-Abl tyrosine kinase of Philadelphia chromosome (Ph1)-positive human leukemias. Bap-1 is a substrate for the Bcr serine-threonine kinase and is also phosphorylated on tyrosine by Bcr-Abl but not by c-Abl. Bap-1 may function in the regulation of c-Bcr and may contribute to the transforming activity of Bcr-Abl in vivo. 14-3-3 proteins are essential for cell proliferation and have a role in determining the timing of mitosis in yeast. Through direct binding to sequences present in Bcr and in other proteins implicated in signaling, the mammalian 14-3-3 proteins may link specific signaling protein components to mitogenic and cell-cycle control pathways.

Association of the protein kinases c-Bcr and Bcr-Abl with proteins of the 14-3-3 family

In this study, a protein that interacts with sequences encoded by the first exon of the protein kinase Bcr was cloned. The Bcr-associated protein 1 (Bap-1) is a member of the 14-3-3 family of proteins. Bap-1 interacts with full-length c-Bcr and with the chimeric Bcr-Abl tyrosine kinase of Philadelphia chromosome (Ph1)-positive human leukemias. Bap-1 is a substrate for the Bcr serine-threonine kinase and is also phosphorylated on tyrosine by Bcr-Abl but not by c-Abl. Bap-1 may function in the regulation of c-Bcr and may contribute to the transforming activity of Bcr-Abl in vivo. 14-3-3 proteins are essential for cell proliferation and have a role in determining the timing of mitosis in yeast. Through direct binding to sequences present in Bcr and in other proteins implicated in signaling, the mammalian 14-3-3 proteins may link specific signaling protein components to mitogenic and cell-cycle control pathways.

Interaction of the protein kinase Raf-1 with 14-3-3 proteins

Members of a family of highly conserved proteins, termed 14-3-3 proteins, were found by several experimental approaches to associate with Raf-1, a central component of a key signal transduction pathway. Optimal complex formation required the amino-terminal regulatory domain of Raf-1. The association of 14-3-3 proteins and Raf-1 was not substantially affected by the activation state of Raf.

Shanghai, China, has the lowest confirmed incidence of childhood diabetes in the world

OBJECTIVE

To determine the incidence of insulin-dependent diabetes mellitus in 0- to 14-year-old children in Shanghai, China, from 1980 to 1991.

RESEARCH DESIGN AND METHODS

Data were collected from hospitals with pediatric departments. The secondary source of validation was primary and middle schools.

RESULTS

The average crude annual incidence rate was 0.61/100,000 (95% confidence interval, 0.48-0.77). The ascertainment-corrected incidence rates were 0.72/100,000 (0.57-0.91).

CONCLUSIONS

The incidence of childhood diabetes in Shanghai, China, was one of the lowest, if not the lowest, in the world.

Lung cancer among tin miners in southeast China: silica exposure, silicosis, and cigarette smoking

The Dachang Tin Mine is an industrial facility with high rates of lung cancer compared to the resident population in Guangxi province in southern China. Historically, exposure to silica dust was very high in the 1950s, falling in recent years to levels in keeping with international standards. Radon levels in the mine are low. We report the findings of a case-control study nested into a cohort study on miners working in Dachang. Cases of lung cancer among miners incident from 1973-1989 were obtained from local comprehensive medical records covering workers employed at the mine. These were matched approximately 3 to 1 with miners randomly chosen from the district surrounding the mine within the same birth decade. Matched odds ratios of 2.42 (95% confidence limit [CL] 1.3, 4.4) for underground employment, 3.52 (95% CL 1.7, 7.5) for smoking, and 2.04 (95%) CL 1.2, 3.7) for silicosis as determined on chest film were noted. Multifactor analysis of unconditional logistic regression showed that among the risk factors for excess mortality from lung cancer only the years spent drilling underground and the cumulative smoking index (product of daily cigarette consumption and number of years smoking) were independent contributors to risk and there was no interaction observed. The presence of silicosis did not contribute to predicting risk independently of the years spent underground.

Measuring distribution of the ellipsoid of birefringence through the thickness of optical disk substrates

We have measured the birefringence of polycarbonate optical disk substrates, using ellipsometry. For a more comprehensive characterization, the probe beam was incident upon substrates in a wide range of polar angles and from different azimuths relative to track direction (ø). Our measurements show that the ellipsoid of birefringence is tilted in the plane of radial (r) and normal (z) directions. The tilt angle varies through thickness, with a maximum value of approximately 10°. For beams passing through the substrate in the ø-z plane and at large incident angles, this tilt causes significant conversion (up to 100%) between p- and s-polarized components. Distributions of other parameters, such as the values of in-plane and vertical birefringence, are obtained simultaneously in the measurements.

Waiting for radiotherapy in Ontario

PURPOSE

Waiting lists for radiotherapy are a fact of life at many Canadian cancer centers. The purpose of this study was to provide a detailed description of the magnitude of the problem in Ontario.

METHODS AND MATERIALS

The interval between diagnosis and initiation of radiation treatment was calculated for all patients receiving primary radiotherapy for carcinoma of the larynx, cervix, lung, and prostate at seven Ontario cancer centers between 1982 and 1991. The interval between surgery and initiation of postoperative radiotherapy for breast cancer was also calculated over the same period. The intervals between diagnosis and referral (t1), between referral and consultation (t2), and between consultation and initiation of radiotherapy (t3), were analyzed separately to determine where delay occurred.

RESULTS

Median waiting times between diagnosis and initiation of radical treatment for carcinoma of the larynx, carcinoma of the cervix, nonsmall cell lung cancer, and carcinoma of the prostate were 30.3 days, 27.2 days, 27.3 days, and 93.3 days, respectively. The exceptional interval between diagnosis and treatment of prostate cancer was due to much longer delays between diagnosis and referral. The median waiting time between diagnosis and initiation of postoperative radiotherapy for breast cancer was 61.4 days and the median time between the completion of surgery and initiation of postoperative radiotherapy was 57.8 days. There were significant intercenter variations in median waiting times, but in every situation the median waiting time in Ontario as a whole increased steadily between 1982 and 1991. Median waiting times from diagnosis to the start of curative treatment for laryngeal cancer, cervical cancer, nonsmall cell lung cancer, and prostate cancer increased by 178.7%, 105.6%, 158.3%, and 62.9%, respectively. Waiting time from completion of surgery to initiation of postoperative radiotherapy for breast cancer increased by 102.7%. Most of the increase in treatment delay was found in the interval between consultation and initiation of radiotherapy.

CONCLUSIONS

The Committee on Standards of the Canadian Association of Radiation Oncologists recommends that the interval between referral and consultation should not exceed 2 weeks and that the interval between consultation and initiation of radiotherapy should also not exceed 2 weeks. The majority of patients treated in Ontario met both those standards in 1982, but by 1991 few patients received care within the prescribed intervals.

Engineered biosynthesis of novel polyketides: stereochemical course of two reactions catalyzed by a polyketide synthase

A genetically engineered strain expressing the essential components of the tetracenomycin polyketide synthase (tcm PKS) along with the actinorhodin ketoreductase (act KR) was found to produce two new (diastereomeric) aromatic polyketides, designated RM20b and RM20c, in addition to RM20, whose structure was reported earlier [McDaniel, R., Ebert-Khosla, S., Hopwood, D. A., & Khosla, C. (1993) Science 262, 1546-1550]. Spectroscopic and in vivo isotopic labeling analysis of RM20b and RM20c revealed that their polyketide backbones were identical to that of RM20 with respect to chain length, regiospecificity of ketoreduction, and regiospecificity of the first intramolecular aldol condensation. This is consistent with earlier predictions that the essential components of the PKS--a bifunctional ketosynthase/acyltransferase, a chain length determining factor, and an acyl carrier protein--are responsible for controlling each of these features of the polyketide backbone [McDaniel, R., Ebert-Khosla, S., Hopwood, D. A., & Khosla, C. (1993) Science 262, 1546-1550; McDaniel, R., Ebert-Khosla, S., Hopwood, D. A., & Khosla, C. (1993) J. Am. Chem. Soc. 115, 11671-11675; Fu, H., Ebert-Khosla, S., Hopwood, D. A., & Khosla, C. (1994) J. Am. Chem. Soc. 116, 4166-4170]. In addition, however, RM20b and RM20c possess two unusual features. In both molecules the hydroxyls on sp3 C-9 and C-7 of the first six-membered ring, which arise as a result of ketoreduction and aldol condensation, respectively, are intact, rather than being lost via dehydration. Furthermore, the relative yield of RM20b (in which these hydroxyls are syn) is 7-fold greater than that of RM20c (in which they are anti).(ABSTRACT TRUNCATED AT 250 WORDS)

Association of polyomavirus middle tumor antigen with 14-3-3 proteins

To carry out its transformation function, the middle tumor antigen (MT) of murine polyomavirus associates with a number of cellular proteins involved in regulation of cell proliferation, including pp60c-Src, phosphatidylinositol 3-kinase, protein phosphatase 2A, Src homologous and collagen protein and growth factor receptor-binding protein 2. Here, two additional MT-associated proteins were identified as members of the 14-3-3 family of proteins. Yeast homologs of 14-3-3 proteins have recently been shown to play a role in the timing of mitosis. Thus, regulation of 14-3-3 protein function by MT may contribute to the development of neoplasia.

A single Arabidopsis GF14 isoform possesses biochemical characteristics of diverse 14-3-3 homologues

Arabidopsis cDNA clones of GF14 proteins originally were isolated on the basis of their association with the G-box DNA/protein complex by a monoclonal antibody screening approach. GF14 proteins are homologous to the 14-3-3 family of mammalian proteins. Here we demonstrate that recombinant GF14 omega, one member of the Arabidopsis GF14 protein family, is a dimeric protein that possesses many of the attributes of diverse mammalian 14-3-3 homologues. GF14 omega activates rat brain tryptophan hydroxylase and protein kinase C in a manner similar to the bovine 14-3-3 protein. It also activates exoenzyme S of Pseudomonas aeruginosa as does bovine brain factor activating exoenzyme S (FAS), which is itself a member of 14-3-3 proteins. In addition, GF14 omega binds calcium, as does the human 14-3-3 homologue reported to be a phospholipase A2. These results indicate that a single isoform of this plant protein family can have multiple functions and that individual GF14 isoforms may have multiple roles in mediating signal transductions in plants. However, GF14 omega does not regulate growth in an in vivo test for functional similarity to the yeast 14-3-3 homologue, BMH1. Thus, while a single plant GF14 isoform can exhibit many of the biochemical attributes of diverse mammalian 14-3-3 homologues, open questions remain regarding the physiological functions of GF14/14-3-3 proteins.

Controversies in the management of laryngeal cancer: results of an international survey of patterns of care

Cancer of the larynx is the most prevalent non-cutaneous malignancy of the head neck region and its treatment presents a threat to both natural speech and survival. This study examines the manner in which two separate specialties in the same and different geographic regions vary in their opinions about the treatment of glottic laryngeal cancer. The goal was to define options available to patients and to classify controversies about optimal treatment which might be resolved in clinical trials. Questionnaires depicting different presentations of glottic larynx cancer were mailed to 1649 otolaryngologists and radiation oncologists in North America, Europe and Australasia. Half the doctors were asked to describe their preferred treatment for a patient while the others were asked to imagine that they themselves were the patient. In all the disease situations opinions varied significantly with respect to the treatment modality advised (whether to employ surgical or radiotherapy approaches) and in more extensive disease situations the intention of treatment also varied depending on whether a curative approach should involve conservation or loss of the larynx. Doctors also recommended similar treatment for their patients as they would for themselves. Apart from disease extent the most significant variables influencing recommendations were the physicians' specialty (P = 0.0001) and where they practice (P = 0.0001). These findings demonstrate diversity of opinion which is influenced more profoundly by the traditions of the specialties and geographic location of practice than by the reported results of treatments for laryngeal cancer. Convictions about optimal management have become barriers to the assessment of the relative value of different treatments and to ensuring that patients are fully informed about management options. The profession should regard as a high priority efforts to resolve these therapeutic conflicts which are associated with major differences in quality of life.

Measurement of birefringence for optical recording of disk substrates

We experimentally investigate the birefringence of bare and coated substrates for magneto-optical recording, using ellipsometry at wavelengths of 632.8 and 780 nm. The polarization rotation and ellipticity of reflected or transmitted light are measured for different incident angles and for different orientations of the incident linear polarization. The measured data are then fitted by the MULTILAYER computer program, which solves the Maxwell equations for a plane wave propagating in a multilayer structure. This approach makes it possible to determine, with high accuracy, the orientations of the principal axes of the substrate and the corresponding refractive indices. The results show that one of the principal axes is always along the substrate's normal direction, but the orientations of the in-plane principal axes can be much different from the radial and track directions. A special feature of the ellipsometers that were used is that a glass hemisphere is placed in contact with the substrate to eliminate refraction of the incident beam. This enables a maximum propagation angle of 70° (with respect to the normal) in the substrate and hence increases the measurement sensitivity. Certain anomalies have been observed, which we believe are associated with the variation of birefringence properties along the thickness direction.

Total pelvic exenteration for locally advanced rectal carcinoma

Total pelvic exenteration was performed in 31 patients (30 males and 1 female) who had rectal cancers involving adjoining pelvic structures. Twenty-nine patients had primary tumors and two had recurrent diseases after previous abdominoperineal resection. Preoperative irradiation was used in nine patients with fixed tumors. When performing the surgical procedure, we also actively employed lateral node dissection to make the operation more radical. Three patients (one with primary tumor and two with recurrent) underwent the exenteration with partial sacrectomy because of the sacral involvement and they all died of local failure within 15 months. The overall 5-year survival rate was 52 percent for all patients and 56 percent for those who had primary tumors. The results suggest that total pelvic exenteration with lateral node dissection should be performed for locally advanced rectal cancer if the tumor is not completely fixed to the pelvic wall and preoperative irradiation should be used to convert a fixed tumor to a resectable one.

[Glucocorticoid receptor-like antigen on neuronal plasma membrane of rat brain]

The existence of glucocorticoid receptor-like antigen on the synaptic plasma membrane (SPM) isolated from rat brain was demonstrated by ABC-gold technique. The SPM was first incubated with McAb 250 (a monoclonal antibody to the glucocorticoid receptor) and then biotinylated horse-anti-mouse IgG and streptavidin-gold (SAG) was added in proper order to the reacting system. The gold particles could be visualized on the external surface of neuronal processes under electron microscope. This is the first morphological demonstration of the existence of glucocorticoid receptor-like antigen on neuronal membranes.

The eukaryotic host factor that activates exoenzyme S of Pseudomonas aeruginosa is a member of the 14-3-3 protein family

Exoenzyme S (ExoS), which has been implicated as a virulence factor of Pseudomonas aeruginosa, catalyzes transfer of the ADP-ribose moiety of NAD+ to many eukaryotic cellular proteins. Its preferred substrates include Ras and several other 21- to 25-kDa GTP-binding proteins. ExoS absolutely requires a ubiquitous eukaryotic protein factor, termed FAS (factor activating ExoS), for enzymatic activity. Here we describe the cloning and expression of a gene encoding FAS from a bovine brain cDNA library and demonstrate that purified recombinant FAS produced in Escherichia coli activates ExoS in a defined cell-free system. The deduced amino acid sequence of FAS shows that the protein (245 residues, calculated molecular mass 27,743 Da) belongs to a highly conserved, widely distributed eukaryotic protein family, collectively designated as 14-3-3 proteins. Various functions have been reported for members of the 14-3-3 family, including phospholipase A2 activity and regulation of tyrosine hydroxylase, tryptophan hydroxylase, and, possibly, protein kinase C activities. Identification of FAS as a 14-3-3 protein establishes an additional function for this family of proteins--the activation of an exogenous ADP-ribosyltransferase. Elucidation of the precise role of FAS in activating ExoS will contribute to understanding the molecular mechanisms by which P. aeruginosa causes disease.

[Dynamic study on superficial blood flow in patients with acute myocardial infarction]

Fourteen points superficial bloodflow (SBF) of the skin and tongue in 55 patients with acute myocardial infarction (AMI) were measured at 12, 24, 36, 48, 60 hours and 3, 5, 7, 10, 14, 21, 28 days after AMI by LDF (PF2). The dynamic study on multiple points SBF of 576 times showed that (1) The mean SBF of skin was 1.0 +/- 0.04 (V) at 12 hours after AMI. It occupied 70.5% in the normal control. After therapy at 48 hours of AMI, the mean SBF was increased to 1.20 +/- 0.03 (V), and approximated 85.9% of the control. (2) The mean SBF in patients with cardiogenic shock was 1.04 +/- 0.05 (V), and it was significantly lower than that without complications (P less than 0.01). The mean SBF showed a negative correlation with the nailfold microcirculatory values (P less than 0.0025). There was a negative correlation between "Tanzhong" SBF and cardiac muscle enzyme CPK, GOT, LDH (P less than 0.05). (3) The SBF of acupuncture point "Tanzhong, Erxin" related to the heart might more sensitively represent the cardiac condition in AMI. (4) The SBF of tongue was negatively correlated with GOT (P less than 0.05). (5) Continual peripheral microcirculatory observation and electrocardiographic monitoring would be helpful in the diagnosis and treatment of earlier complications of AMI in order to reduce the mortality.

[Arnold-Chiari malformation presenting in adult life]

Eleven patients of Arnold-Chiari malformation (ACM) in adults were reported. Nine of them associated with syringomyelia. The etiology, clinical features, diagnosis, differential diagnosis, the findings of SSEP, MEP, EMG, NCV, and the treatment of ACM in adults were discussed. Our observations lead us to consider that both clinical symptoms and examinations are crucial in the diagnosis. In addition, the delineation of ACM in adults with or without syringomyelia can be somewhat difficult by traditional radiological examinations, but can be readily demonstrated by MRI.

[Estimation of glucocorticoid membrane binding sites in synaptic plasma membrane isolated from porcine brain]

Using radioligand binding assay, we measured the Bmax and Kd of glucocorticoid membrane binding sites (GCMBS) in the synaptic plasma membranes isolated from different regions of porcine brain. The Kds of GCMBS in cerebrum, cerebellum, midbrain, thalamus, nuclei caudatus and hypothalamus are all around 200 nmol/L. The Bmax of GCMBS in the mentioned brain regions ranges from 218.98 fmol/mg to 486.95 fmol/mg protein.

Molecular cytogenetic study of short arm aberrations in human D, G group chromosomes

Six cases of Dp+/Gp+, 10 cases of D/G translocation, 1 case of supernumerary marker chromosome, and 1 case of Yqs were studied using molecular and cytogenetic techniques. The Ag-NOR frequencies of the Dp+ and Gp+ groups were found to be higher than those of normal controls, while their satellite association frequencies were lower. Autoradiographic silver grains were not significantly distributed along the p+ part of the marker chromosome as revealed by chromosomal in situ hybridization using an rRNA probe. This result differs from our previous report. It is suggested that there might be different mechanisms for the formation of p+ on acrocentric chromosomes. D/G translocation cases were found to have lost their NOR. A study of supernumerary marker chromosomes and Yqs cases suggested that the marker chromosome and Yqs exerted no phenotypic effect. The mechanism of their formation is discussed.

An improved Tn7-based system for the single-copy insertion of cloned genes into chromosomes of gram-negative bacteria

A system is described for the single-copy, stable insertion of cloned DNA sequences into the chromosomes of Gram- bacteria. Two narrow-host-range plasmids form the basis of this system: the 'carrier' plasmid contains the mini Tn7-Km transposon, into which foreign DNA can be cloned; the 'helper' plasmid provides the Tn7 transposition functions in trans. Both plasmids are readily transferred into Gram- bacteria by conjugation. The functionality of this system has been demonstrated in Rhodospirillum rubrum.