Étude par r.m.n. de quatre disaccharides peracétylés sélectivement enrichis en 13C

Four peracetylated disaccharides ¹³C-labelled at the C-1′ position and having α-d-(1′→3), β-d-(1′→3), α-d-(1′→4), and β-d-(1′→4) linkages were prepared starting from the commercially available d-[1-¹³C]glucose. They were studied on the basis of their ³J_¹³CH coupling constants in relation with the conformation in solution of oligosaccharides as models for the corresponding polymer. A method of analysis of the n.m.r. spectra is described and the coupling constants J_{¹³C-1′H} given, particularly the ²J coupling (in the same cycle and with sign determination) and the ³J coupling (through the glycosidic bond). In that case, the values obtained give experimental information on the ψ angle values. They are compared with the known X-ray data for similar compounds.     

Nonparallelism in MHCIIβ diversity accompanies nonparallelism in pathogen infection of lake whitefish (Coregonus clupeaformis) species pairs as revealed by next‐generation sequencing

Major histocompatibility (MHC) immune system genes may evolve in response to pathogens in the environment. Because they also may affect mate choice, they are candidates for having great importance in ecological speciation. Here, we use next‐generation sequencing to test the general hypothesis of parallelism in patterns of MHCIIβ diversity and bacterial infections among five dwarf and normal whitefish sympatric pairs. A second objective was to assess the functional relationships between specific MHCIIβ alleles and pathogens in natural conditions. Each individual had between one and four alleles, indicating two paralogous loci. In Cliff Lake, the dwarf ecotype was monomorphic for the most common allele. In Webster Lake, the skew in the allelic distribution was towards the same allele but in the normal ecotype, underscoring the nonparallel divergence among lakes. Our signal of balancing selection matched putative peptide binding region residues in some cases, but not in others, supporting other recent findings of substantial functional differences in fish MHCIIβ compared with mammals. Individuals with fewer alleles were less likely to be infected; thus, we found no evidence for the heterozygote advantage hypothesis. MHCIIβ alleles and pathogenic bacteria formed distinct clusters in multivariate analyses, and clusters of certain alleles were associated with clusters of pathogens, or sometimes the absence of pathogens, indicating functional relationships at the individual level. Given that patterns of MHCIIβ and bacteria were nonparallel among dwarf and normal whitefish pairs, we conclude that pathogens driving MHCIIβ evolution did not play a direct role in their parallel phenotypic evolution.     

Algorithms and software for support of gene identification experiments

MOTIVATION: Gene annotation is the final goal of gene prediction algorithms. However, these algorithms frequently make mistakes and therefore the use of gene predictions for sequence annotation is hardly possible. As a result, biologists are forced to conduct time-consuming gene identification experiments by designing appropriate PCR primers to test cDNA libraries or applying RT-PCR, exon trapping/amplification, or other techniques. This process frequently amounts to 'guessing' PCR primers on top of unreliable gene predictions and frequently leads to wasting of experimental efforts. RESULTS: The present paper proposes a simple and reliable algorithm for experimental gene identification which bypasses the unreliable gene prediction step. Studies of the performance of the algorithm on a sample of human genes indicate that an experimental protocol based on the algorithm's predictions achieves an accurate gene identification with relatively few PCR primers. Predictions of PCR primers may be used for exon amplification in preliminary mutation analysis during an attempt to identify a gene responsible for a disease. We propose a simple approach to find a short region from a genomic sequence that with high probability overlaps with some exon of the gene. The algorithm is enhanced to find one or more segments that are probably contained in the translated region of the gene and can be used as PCR primers to select appropriate clones in cDNA libraries by selective amplification. The algorithm is further extended to locate a set of PCR primers that uniformly cover all translated regions and can be used for RT-PCR and further sequencing of (unknown) mRNA.      

Le group trichloroacétyle comme substituant temporaire; synthése du gentiotétraose

Glycosylation of 1,2,3,4-tetra-O-acetyl-β-d-glucopyranose with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide and 2,3,4-tri-O-acetyl-6-O-trichloroacetyl-α-d-glucopyranosyl bromide, in the presence of mercuric cyanide, is 96–98% stereospecific. The trichloroacetyl group has been used as a temporary protecting group in a sequential synthesis of gentiotriose and gentiotetraose derivatives, first in homogeneous phase, and subsequently on a polymeric support: in the latter case the yield is about 70%.     

Bacterial biosynthesis of cellulose from d-glucose or glycerol precursors labelled with deuterium

d-Glucose and glycerol precursors randomly labelled with deuterium were prepared and used for the biosynthesis of bacterial cellulose by Acetobacter xylinum. The materials obtained were converted into triacetate derivatives and analysed by 250 MHz nuclear magnetic resonance.Labelling percentages on each position are reported. The weighted addition of combinations of different ²H or ¹H sites for mixtures of multiple labelled compounds was performed by means of an N.M.R. spectrum simulation program according to different hypotheses. The nonrandom nature of the results showed the importance of exchange phenomena and of the biosynthetic pathways which take place during cellulose biosynthesis.While showing less favourable properties than ¹³C enrichment, deuterium labelling can nevertheless lead to significant results (in particular if one is dealing with labelled fragments of precursors incorporated partly or totally into a final molecule), particularly in view of the easy preparation of deuterated compounds by catalytic exchange.