Linkage disequilibrium studies in multiple endocrine neoplasia type 1 (MEN1)

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterised by tumours of the parathyroids, pancreas and anterior pituitary. The MEN1 gene has been localised to a 2-Mb region of chromosome 11q13 by meiotic mapping studies in MEN1 families. Such studies may have a limited resolution of approximately 1 cM (i.e. 1 Mb) and we have therefore investigated 96 MEN1 families (40 British, 17 French, 12 Finnish, 7 Swedish, 7 Dutch, 7 North American, 2 Australian, 1 New Zealand, 1 German, 1 Spanish and 1 Danish) for linkage disequilibrium, in order to facilitate a finer mapping resolution. We have utilised five microsatellite DNA sequence polymorphisms from the candidate region and have accurately determined their allele sizes, which ranged from 161 bp to 272 bp. The heterozygosity and number of alleles (given in brackets), respectively, at the loci were: D11S1883 (76%, 11), D11S457 (55%, 5), PYGM (94%, 18), D11S1783 (10%, 4) and D11S449 (87%, 16). Allelic association was assessed by Chi-square 2 ×n contingency tables, by Fisher exact 2 ×n contingency tables and by a likelihood-based approach. The results of haplotype analysis revealed 91 different affected haplotypes in the 96 families, an identical affected haplotype being observed in no more than two families. These results indicate the absence of an ancestral affected haplotype. Significant linkage disequilibrium (P < 0.005) could be established amongst the microsatellite loci but not between the loci and MEN1 in either the total population or in any of the geographical sub-populations. The absence of linkage disequilibrium between MEN1 and the polymorphic loci is probably the result of the occurrence of multiple different disease-causing mutations in MEN1. Received: 1 April 1997 / Accepted: 25 June 1997     

Some new variants of serum protease inhibitors in Meishan pigs

Serum samples of Meishan (13 animals) and Meishan x Wild Boar crosses (361 animals) were analysed by means of two-dimensional electrophoresis. Some new variants in protease inhibitor systems PO1A, PO1B and PI2 are reported.     

Identification of 3-hydroxypalmitic acid methyl ester as a novel autoregulator controlling virulence in Ralstonia solanacearum

Expression of virulence genes in Ralstonia solanacearum , a phytopathogenic bacterium, is controlled by a complex regulatory network that integrates multiple signal inputs. Production of several virulence determinants is co-ordinately reduced by inactivation of phcB , but is restored by growth in the presence of a volatile extracellular factor (VEF) produced by wild-type strains of R. solanacearum . The VEF was purified from spent culture broth by distillation, solvent extraction, and liquid chromatography. Gas chromatography and mass spectroscopy identified 3-hydroxypalmitic acid methyl ester (3-OH PAME) as the major component in the single peak of VEF activity. Authentic 3-OH PAME and the purified VEF were active at ≤1 nM, and had nearly equivalent specific activities for stimulating the expression of eps (the biosynthetic locus for extracellular polysaccharide) in a phcB mutant. Authentic 3-OH PAME also increased the production of three virulence factors by a phcB mutant over 20-fold to wild-type levels, restored normal cell density-associated expression of eps and increased expression of eps when delivered via the vapour phase. Reanalysis of the PhcB amino acid sequence suggested that it is a small-molecule S -adenosylmethionine-dependent methyltransferase, which might catalyse synthesis of 3-OH PAME from a naturally occurring fatty acid. Biologically active concentrations of extracellular 3-OH PAME were detected before the onset of eps expression, suggesting that it is an intercellular signal that autoregulates virulence gene expression in wild-type R. solanacearum . Other than acyl-homoserine lactones, 3-OH PAME is the only endogenous fatty acid derivative shown to be an autoregulator and may be the first example of a new family of compounds that can mediate long-distance intercellular communication.     

Microphotometric determination of structure-bound oxidoreductase activities avoiding nothing-dehydrogenase artefacts: succinate dehydrogenase

 A tetrazolium-based microphotometric method has been devised for the determination of structure-bound dehydrogenase activities with correction for nothing-dehydrogenase artefacts. The method is based on the microphotometric recording of maximum reaction rates in a simple incubation chamber and consists of two successive measurements on the same section, the first in the absence and the second in the presence of the substrate. Following the first measurement, the substrate-free medium is quickly exchanged with the substrate-containing medium and a second measurement is taken. Subtraction of the first from the second reaction rate yields the enzyme activity corrected for nothing-dehydrogenase. Measurements of succinate dehydrogenase (SDH) in skeletal muscle fibres, liver, cardiac atrium and ventricle demonstrate the feasibility of the method. Measurements on the extensor digitorum longus muscle of rat reveal a range of up to fivefold differences in SDH activity within the fibre population of this muscle. Accepted: 11 April 1997     

An imported thylakoid protein accumulates in the stroma when insertion into thylakoids is inhibited

The light-harvesting chlorophyll a/b protein (LHCP) is synthesized in the cytosol as a precursor (pLHCP) that is imported into chloroplasts and assembled into thylakoid membranes. Under appropriate conditions, either pLHCP or LHCP will integrate into isolated thylakoids. We have identified two situations that inhibit integration in this assay. Ionophores and uncouplers inhibited integration up to 70%. Carboxyl-terminal truncations of pLHCP also interfered with integration. A 22-residue truncation reduced integration to about 25% of control, whereas a 93 residue truncation completely abolished it. When pLHCP was imported into chloroplasts in the presence of uncouplers or when truncated forms of pLHCP were used, significant amounts of the imported proteins failed to insert into thylakoids and instead accumulated in the aqueous stroma. Accumulation of stromal LHCP occurred at uncoupler concentrations required to dissipate the trans-thylakoid proton electrochemical gradient and was enhanced at reduced levels of ATP. The latter effect may be a secondary consequence of a reduction in ATP-dependent degradation within the stroma. These results indicate that the stroma is an intermediate location in the LHCP assembly pathway and provide the first evidence for a soluble intermediate during biogenesis of a chloroplast membrane protein.