Pierre Brignon

Two‐dimensional gel analysis of the proteome of lager brewing yeasts

Modern lager brewing yeasts used in beer production are hybrid strains consisting of at least two different genomes. To obtain information on the identity of the parental strains that gave rise to industrial lager yeasts, we used two‐dimensional (2‐D) gel electrophoresis and analysed the proteomes of different Saccharomyces species isolated from breweries. We found that the proteome of lager brewing yeasts and of the type strains of S. carlsbergensis, S. monacensis and S. pastorianus can be interpreted as the superimposition of two elementary patterns. One originates from proteins encoded by a S. cerevisiae‐like genome. The other corresponds to a divergent Saccharomyces species whose best representative is a particular S. pastorianus strain, NRRL Y‐1551. A map of industrial lager brewing yeasts has been established, with the individual origin of proteins and with identification of protein spots by comparison to known S. cerevisiae proteins. This 2‐D map can be accessed on the Lager Brewing Yeast Protein Map server through the World Wide Web. This study provides the first example of the use of proteome analysis for investigating taxonomic relationships between divergent yeast species. Copyright

A family of laboratory strains of Saccharomyces cerevisiae carry rearrangements involving chromosomes I and III

In order to study meiotic segregation of chromosome length polymorphism in yeast, we analysed the progeny of a cross involving two laboratory strains FL100trp and YNN295. Analysis of the parental strains led us to detect an important length polymorphism of chromosomes I and III in FL100trp. A reciprocal translocation involving 80 kb of the left arm of chromosome III and 45 kb of the right arm of chromosome I was shown to be the cause for the observed polymorphism in this strain. The characterization of the translocation breakpoints revealed the existence of a transposition hot‐spot on chromosome I: the sequence of the translocation joints on chromosomes I and III suggests that the mechanism very likely involved homologous recombination between Ty2 transposable elements on each chromosome. Analysis of FL100, FL200 and FL100trp ura, which are related to FL100trp, shows that this reciprocal translocation is present in some of the strains of the FL series, whereas the parental strain FL100 does not carry the same rearrangement. We evidenced instead the duplication of 80 kb of chromosome III on chromosome I and a deletion of 45 kb of the right arm of chromosome I in this strain, indicating that secondary events might have taken place and that the strain currently named FL100 is not the common ancestor of the FL series.