Reaction of a nucleoside 2, 4-dinitrophenyl phosphate with fluoride; a convenient method for the preparation of the nucleoside phosphorfluoridate.

Examination of the reaction of 2, 4-dinitrofluorobenzene with thymidine-5' phosphate in detail reveals that the initial product is the 2, 4-dinitrophenyl ester. This reacts with fluoride to produce thymidine-5' phosphorfluoridate. This second reaction provides the basis for the conversion of preformed thymidine-5' 2, 4-dinitrophenyl phosphate to thymidine-5' phosphorofluoridate.     

Mitochondrial targeting sequences may form amphiphilic helices.

Twenty three mitochondrial targeting sequences have been analysed with regard to their potential for forming amphiphilic helices. It is shown that most if not all of these sequences can be expected to form helices with high hydrophobic moments in a suitable environment. In the few cases studied so far, the segments of maximal hydrophobic moment coincide closely with 'critical' regions defined by deletions and point mutations.     

Sequence differences between glycosylated and non-glycosylated Asn-X-Thr/Ser acceptor sites: implications for protein engineering

In N-glycosylated glycoproteins, carbohydrate is attached to Asn in the sequence Asn-X-Ser/Thr, where X denotes any amino acid. However, the presence of this consensus peptide does not always lead to glycosylation. We have compiled an extensive collection of glycosylated and non-glycosylated Asn-X-Thr/Ser sites and present a statistical study based on this data set. Our results indicate that non-glycosylated sites tend to be found more frequently towards the C termini of glycoproteins, and that proline residues in positions X and Y in the consensus Asn-X-Thr/Ser-Y strongly reduce the likelihood of N-linked glycosylation. Beyond this, there are no obvious local sequence features that seem to correlate with the absence or presence of N-linked glycosylation. These findings are discussed in terms of the prediction and engineering of glycosylation sites in secretory proteins.     

Molecular characterization of three Mhc class II B haplotypes in the ring-necked pheasant

We investigated the class II B genes in free-ranging population of the ring-necked pheasant Phasianus colchicus by a combination of restriction fragment length polymorphism (RFLP), polymerase chain reaction (PCR), and DNA sequencing. Special attention was paid to the variation in the second exon, which encodes the peptide-binding ₁-domain. The population was introduced, but it still exhibited major histocompatibility complex polymorphism with at least three segregating class II B haplotypes and consequently six genotypes. We found two class II B genes associated with each haplotype. The class II B genes of birds had until then only been molecularly characterized in the domestic chicken. the pheasant genes were highly variable, although one of the amplified sequences was found in two different haplotypes. Taken together, the most polymorphic positions (residues 37 and 38) were not identical in any of the predicted protein sequences, but all except one of the motifs had already been foud in the domestic chicken. Structurally important features in mammalian class II B genes were generally conserved also in the pheasant sequences, but the loss of a potential salt bridge constituent (Arg₇₂) in several sequences may suggest a slightly different structure of the adjacent parts of the peptide-binding groove. The pheasant genes are most closely related to the so called B-LBII family in the chicken, indicating that this represents a major line of development among avian class II B genes.The nucleotide sequence data reported in this paper have been submitted to the EMBL nucleotide sequence database and have been assigned the accession numbers X75403-X75407. Correspondence to: H. Wittzell, Department of Theoretical Ecology, Ecology Building, Lund University, S-223 62 Lund, Sweden.     

Contrast-enhancement cardiac magnetic resonance imaging beyond the scope of viability

The clinical applications of cardiovascular magnetic resonance imaging with contrast enhancement are expanding. Besides the direct visualisation of viable and non-viable myocardium, this technique is increasingly used in a variety of cardiac disorders to determine the exact aetiology, guide proper treatment, and predict outcome and prognosis. In this review, we discuss the value of cardiovascular magnetic resonance imaging with contrast enhancement in a range of cardiac disorders, in which this technique may provide insights beyond the scope of myocardial viability.