Abnorme Kätzchenbildungen beiSalix caprea L. und beiSalix cinerea L.

Ohne Zusammenfassung     

Correspondence regarding October 31, 2003, Breakthroughs and Views by K. Brown and P.L. Carmichael

A. Fuglsang [Biochem. Biophys. Res. Commun. 317 (2004) 957-964] suggested that effective number of codons for individual amino acids (Nc-values) should be re-adjusted to the number of synonymous codons of those amino acids, in order to prevent the overestimation of the effective number of codons. Here, it is shown that re-adjustment at the level of individual amino acids results in loss of considerable amounts of information. Furthermore, we have shown that theoretical Nc-values are functions of GC3s (and GC1s); as a result, when an amino acid Nc-value exceeds the related theoretical Nc-value, the implication of re-adjustment depends on the GC composition of the gene.     

Structural diversity of the classical H-2 genes: K, D, and L.

Twenty-three class I DNA sequences, representing alleles of the H-2K, D, and L loci, were analyzed to assess patterns of nucleotide and amino acid diversity. Comparisons of the allelic and nonallelic sequences revealed locus specificity in regions encoding the leader peptides and the carboxyl-terminal segments of the Ag presenting molecules. Analyses focusing on the sequences that determine the Ag binding domains revealed weak or insignificant allelic associations, a finding that is in sharp contrast to previously observed relationships among the homologous human sequences. The amino acid positions exhibiting high diversity in the encoded glycoproteins in both mice and humans are localized primarily to the Ag binding site. In the mouse, diverse amino acids were positioned similarly in the K and D/L glycoproteins, although in humans, the A and B glycoproteins exhibit distinctive differences in their locations within the Ag binding site. The absence of locus specificity among the sequences that determine the Ag binding domains of the mouse is consistent with the hypothesis that ectopic gene conversion leads to interlocus exchange of class I sequences. Comparable interlocus exchanges among human class I genes have not played a similar role in shaping human A and B sequences. The basis of this difference between mice and humans is not clear. The nature of amino acid substitutions distinguishing class I loci in mice and humans are comparable, and the role of natural selection in determining diversity appears to be similar in the two species.     

Picrasin K,a new quassinoid from Quassia amara L. (Simaroubaceae)

A new quassinoid Picrasin K 1 was isolated from a decoction made of Quassia amara leaves, traditionally used in French Guyana to treat malaria. The structure and relative stereochemistry of 1 was determined through extensive NMR analysis. Picrasin K showed a low activity against Plasmodium falciparum in vitro (IC₅₀ = 8 μM), and a similar low activity on human cancerous cells line (IC₅₀ = 7 μM on MCF-7 cells line).