Analysis of the genes flanking xabB: a methyltransferase gene is involved in albicidin biosynthesis in Xanthomonas albilineans

Transposon mutagenesis and complementation studies previously identified a gene (xabB) for a large (526 kDa) polyketide-peptide synthase required for biosynthesis of albicidin antibiotics and phytotoxins in the sugarcane leaf scald pathogen Xanthomonas albilineans. A cistron immediately downstream from xabB encodes a polypeptide of 343 aa containing three conserved motifs characteristic of a family of S-adenosyl-L-methionine (SAM)-dependent O-methyltransferases. Insertional mutagenesis and complementation indicate that the product of this cistron (designated xabC) is essential for albicidin production, and that there is no other required downstream cistron. The xab promoter region is bidirectional, and insertional mutagenesis of the first open reading frame (ORF) in the divergent gene also blocks albicidin biosynthesis. This divergent ORF (designated thp) encodes a protein of 239 aa displaying high similarity to several IS21-like transposition helper proteins. The thp cistron is not located in a recognizable transposon, and is probably a remnant from a past transposition event that may have contributed to the development of the albicidin biosynthetic gene cluster. Failure of 'in trans' complementation of rhp indicates that a downstream cistron transcribed with thp is required for albicidin biosynthesis. (C) 2000 Elsevier Science B.V. All rights reserved.

Magnetic resonance imaging and diseases of the liver and biliary tract. Part 2. Magnetic resonance cholangiography and angiography and conclusions

Magnetic resonance cholangiography (MRC) relies on the strong T-2 signal from stationary liquids, in this case bile, to generate images. No contrast agents are required, and the failure rate and risk of serious complications is lower than with endoscopic retrograde cholangiopancreatography (ERCP). Data from MRC can be summated to produce an image much like the cholangiogram obtained by using ERCP. In addition, MRC and conventional MRI can provide information about the biliary and other anatomy above and below a biliary obstruction. This provides information for therapeutic intervention that is probably most useful for hilar and intrahepatic biliary obstruction. Magnetic resonance cholangiography appears to be similar to ERCP with respect to sensitivity and specificity in detecting lesions causing biliary obstruction, and in the diagnosis of choledocholithiasis. It is also suited to the assessment of biliary anatomy (including the assessment of surgical bile-duct injuries) and intrahepatic biliary pathology. However, ERCP can be therapeutic as well as diagnostic, and MRC should be limited to situations where intervention is unlikely, where intrahepatic or hilar pathology is suspected, to delineate the biliary anatomy prior to other interventions, or after failed or inadequate ERCP. Magnetic resonance angiography (MRA) relies on the properties of flowing liquids to generate images. It is particularly suited to assessment of the hepatic vasculature and appears as good as conventional angiography. It has been shown to be useful in delineating vascular anatomy prior to liver transplantation or insertion of a transjugular intrahepatic portasystemic shunt. Magnetic resonance angiography may also be useful in predicting subsequent variceal haemorrhage in patients with oesophageal varices. (C) 2000 Blackwell Science Asia Pty Ltd.

C-13-NMR, H-1-NMR, and FT-Raman study of radiation-induced modifications in radiation dosimetry polymer gels

H-1- and C-13-NMR spectroscopy and FT-Raman spectroscopy are used to investigate the properties of a polymer gel dosimeter post-irradiation. The polymer gel (PACT) is composed of acrylamide, N,N'-methylene-bisacrylamide, gelatin, and water. The formation of a polyacrylamide network within the gelatin matrix follows a dose dependence nonlinearly correlated to the disappearance of the double bonds from the dissolved monomers within the absorbed dose range of 0-50 Gy. The signal from the gelatin remains constant with irradiation. We show that the NMR spin-spin relaxation times (T-2) of PAGs irradiated to up to 50 Gy measured in a NMR spectrometer and a clinical magnetic resonance imaging scanner can be modeled using the spectroscopic intensity of the growing polymer network. More specifically, we show that the nonlinear T-2 dependence against dose can be understood in terms of the fraction of protons in three different proton pools. (C) 2000 John Wiley & Sons, Inc.

Structure revision and assignment of absolute stereochemistry of a marine C-21 bisfuranoterpene

The C-21 bisfuranoterpene (-)-isotetradehydrofurospongin-1 (6), previously isolated from a Western Australian Spongia sp., has been reisolated from a specimen of Spirastrella papilosa collected during scientific trawling operations in the Great Australian Eight. A 2D NMR analysis of 6 has prompted reassignment of the published structure 5, while degradation and chiral HPLC analysis have allowed determination of the absolute stereochemistry.

Phorbasin B and C: Novel diterpenes from a southern Australian marine sponge, Phorbas species

A southern Australian Phorbas sp. has yielded the novel diterpenes phorbasin B (2) and phorbasin C (3). Phorbasins B and C possess a hitherto unknown carbon skeleton, and their structures were assigned on the basis of detailed spectroscopic analyses.

Mutation screening of the c-MYB negative regulatory domain in acute and chronic myeloid leukaemia

Over-expression of the c-myb gene and expression of activated forms of myb are known to transform haemopoietic cells, particularly cells of the myeloid lineage. Truncations or mutations that disrupt the negative regulatory domain (NRD) of the Myb protein confer an increased ability to transform cells. Although it has proved difficult to link mutations in c-MYB to human leukaemia, no studies investigating the presence of mutations within the c-MYB NRD have been reported. Therefore, we have performed mutational analysis of this region, using polymerase chain reaction-single-stranded conformation polymorphism and sequence analysis, in 26 patients with acute or chronic myeloid leukaemia, No mutations were detected, indicating that mutation of this region of the Myb protein is not common in the pathogenesis or progression of these diseases.

Weight reduction improves biochemistry and histology in patients with chronic hepatitis C

Hepatitis C virus (HCV) is a major cause of chronic liver disease that may progress to cirrhosis. Antiviral treatment is successful in less than 50% of patients, is costly and causes debilitating side effects. For these reasons, additional therapies to limit the progression of liver disease are urgently required. Steatosis is found in 60% of patients with HCV and is strongly associated with more severe fibrosis. Improvements in biochemical parameters may be seen with weight reduction, however the effects on liver histology have not been investigated. We propose that in patients with chronic HCV and steatosis, obesity contributes to fat in the liver, which results in increased fibrosis and progression to cirrhosis. This study investigated the effect of weight reduction on liver biochemistry and histology in patients with HCV and the success of weight maintenance after an intensive intervention. We examined the effect of a 12 week diet and exercise program where all subjects were seen weekly by the Dietician, with the goal of achieving a 0.5 kg weight loss per week. Biochemistry was monitored monthly and a liver biopsy was performed prior to and 3-6 months after the intervention period. Patients then entered a 12 month weight maintenance program with monthly dietetic review. After 12 weeks there was a mean weight loss of 5.9 ± 3.2 kg and a mean reduction in waist circumference of 9.0 ± 5.0 cm. In 16 of the 19 patients, serum ALT levels fell progressively with weight loss. Mean fasting insulin fell from 16 to 11 mmol/L (p

Influence of patient age and implantation technique on the probability of re-replacement of the homograft aortic valve

Background and aim of the study: Results of valve re-replacement (reoperation) in 898 patients undergoing aortic valve replacement with cryopreserved homograft valves between 1975 and 1998 are reported. The study aim was to provide estimates of unconditional probability of valve reoperation and cumulative incidence function (actual risk) of reoperation. Methods: Valves were implanted by subcoronary insertion (n = 500), inclusion cylinder (n = 46), and aortic root replacement (n = 352). Probability of reoperation was estimated by adopting a mixture model framework within which estimates were adjusted for two risk factors: patient age at initial replacement, and implantation technique. Results: For a patient aged 50 years, the probability of reoperation in his/her lifetime was estimated as 44% and 56% for non-root and root replacement techniques, respectively. For a patient aged 70 years, estimated probability of reoperation was 16% and 25%, respectively. Given that a reoperation is required, patients with non-root replacement have a higher hazard rate than those with root replacement (hazards ratio = 1.4), indicating that non-root replacement patients tend to undergo reoperation earlier before death than root replacement patients. Conclusion: Younger patient age and root versus non-root replacement are risk factors for reoperation. Valve durability is much less in younger patients, while root replacement patients appear more likely to live longer and hence are more likely to require reoperation.

Conformations of platypus venom C-type natriuretic peptide in aqueous solution and sodium dodecyl sulfate micelles

Nuclear magnetic resonance spectroscopy was used to investigate the conformations of the platypus venom C-type natriuretic peptide A (OvCNPa) in aqueous solutions and in solutions containing sodium dodecyl sulfate (SDS) micelles. The chemically synthesized OvCNPa showed a substantial decrease in flexibility in aqueous solution at 10 degreesC, allowing the observation of medium- and long-range nuclear Overhauser enhancement (NOE) connectivities. Three-dimensional structures calculated using these data showed flexible and reasonably well-defined regions, the locations of which were similar in the two solvents. In aqueous solution, the linear part that spans residues 3-14 was basically an extended conformation while the cyclic portion, defined by residues 23-39, contained a series of beta-turns. The overall shape of the cyclic portion was similar to that observed for an atrial natriuretic peptide (ANP) variant in aqueous solution. OvCNPa adopted a different conformation in SDS micelles wherein the N-terminal region, defined by residues 2-10, was more compact, characterised by turns and a helix, while the cyclic region had turns and an overall shape that was fundamentally different from those structures observed in aqueous solution. The hydrophobic cluster, situated at the centre of the ring of the structure in aqueous solution, was absent in the structure in the presence of SDS micelles. Thus, OvCNPa interacts with SDS micelles and can possibly form ion-channels in cell membranes. (C) 2002 Elsevier Science Ltd. All rights reserved.

D-amino acid residue in the C-type natriuretic peptide from the venom of the mammal, Ornithorhynchus anatinus, the Australian platypus

The C-type natriuretic peptide from the platypus venom (OvCNP) exists in two forms, OvCNPa and OvCNPb, whose amino acid sequences are identical. Through the use of nuclear magnetic resonance, mass spectrometry, and peptidase digestion studies, we discovered that OvCNPb incorporates a D-amino acid at position 2 in the primary structure. Peptides containing a D-amino acid have been found in lower forms of organism, but this report is the first for a D-amino acid in a biologically active peptide from a mammal. The result implies the existence of a specific isomerase in the platypus that converts an L-amino acid residue in the protein to the D-configuration. (C) 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

maT - A clade of transposons intermediate between mariner and Tc1

A group of transposons, named maT, with characteristics intermediate between mariner and Tc1 transposons, is described. Two defective genomic copies of MdmaT from the housefly Musca domestica, with 85% identity, were found flanking and imbedded in the MdalphaE7 esterase gene involved in organophosphate insecticide resistance. Two cDNA clones, with 99% identity to each other and 72%-89% identity to the genomic copies were also obtained, but both represented truncated versions of the putative open reading frame. A third incomplete genomic copy of MdmaT was also identified upstream of the putative M. domestica period gene. The MdmaT sequences showed high identity to the transposable element Bmmar1 from the silk-worm moth, Bombyx mori, and to previously unidentified sequences in the genome of Caenorhabditis elegans. A total of 16 copies of full-length maT sequences were identified in the C elegans genome, representing three variants of the transposon, with 34%-100% identity amongst them. Twelve of the copies, named CemaT1, were virtually identical, with eight of them encoding a putative full length, intact transposase. Secondary structure predictions and phylogenetic analyses confirm that maT elements belong to the mariner-Tc1 superfamily of transposons, but their intermediate sequence and predicted structural characteristics suggest that they belong to a unique clade, distinct from either mariner-like or Tc1-like elements.