The prion protein is known to be a copper-binding protein, but affinity and stoichiometry data for the fulllength protein at a physiological pH of 7 were lacking. Furthermore, it was unknown whether only the highly flexible N-terminal segment with its octarepeat region is involved in copper binding or whether the structured C-terminal domain is also involved. Therefore we systematically investigated the stoichiometry and affinity of copper binding to full-length prion protein PrP 23-231 and to different N-and C-terminal fragments using electrospray ionization mass spectrometry and fluorescence spectroscopy. Our data indicate that the unstructured N-terminal segment is the cooperative copper-binding domain of the prion protein. The prion protein binds up to five copper(II) ions with half-maximal binding at ϳ2 M. This argues strongly for a direct role of the prion protein in copper metabolism, since it is almost saturated at about 5 M, and the exchangeable copper pool concentration in blood is about 8 M.

In a systematic approach to the study of Saccharomyces cerevisiae genes of unknown function, 150 deletion mutants were constructed (1 double, 149 single mutants) and phenotypically analysed. Twenty percent of all genes examined were essential. The viable deletion mutants were subjected to 20 different test systems, ranging from high throughput to highly specific test systems. Phenotypes were obtained for two-thirds of the mutants tested. During the course of this investigation, mutants for 26 of the genes were described by others. For 18 of these the reported data were in accordance with our results. Surprisingly, for seven genes, additional, unexpected phenotypes were found in our tests. This suggests that the type of analysis presented here provides a more complete description of gene function.

Conversion of the cellular isoform of the prion protein (PrP C ) into the pathogenic isoform (PrP Sc ) is thought to be the causative event in prion diseases. Biochemically, PrP Sc differs from PrP C in its partial resistance to proteinase K (PK). The amino acid sequence AGAAAAGA, comprising residues 112-119 of the murine PrP C , has been shown to be amyloidogenic and evolutionarily conserved. To assess the effect of mutations at and around this hydrophobic sequence on protease resistance, the sequence was replaced either by alanines or by glycines and, in a third mutant, a large part surrounding this region was removed. The PrP mutant carrying substitutions of glycines for alanines showed PK resistance and aberrant proteolytic processing. Tetracycline-induced expression of this mutant indicated that resistance to protease is acquired concurrent with the synthesis of the protein. These findings indicate that mutations in the central hydrophobic region lead to immediate alterations in PrP structure and processing.