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Sequencing of the yeast genome has shown that about one-third of the yeast ORFs code for unknown proteins. Many other have similarity to known genes, but still the cellular functions of the gene products are unknown. The aim of the B1 Consortium of the EUROFAN project was to perform a qualitative phenotypic analysis on yeast strains deleted for functionally orphan genes. To this end we set up a simple approach to detect growth defects of a relatively large number of strains in the presence of osmolytes, ethanol, high temperature, inhibitory compounds or drugs affecting protein biosynthesis, phosphorylation level or nucleic acids biosynthesis. We have now developed this procedure to a semi-quantitative level, we have included new inhibitors, such as hygromycin B, benomyl, metals and additional drugs interfering with synthesis of nucleic acids, and we have performed phenotypic analysis on the deleted strains of 564 genes poorly characterized in respect to their cellular functions. About 30% of the deleted strains showed at least one phenotype: many of them were pleiotropic. For many gene deletions, the linkage between the deletion marker and the observed phenotype(s) was studied by tetrad analysis and their co-segregation was demonstrated. Co-segregation was found in about two-thirds of the analysed strains showing phenotype(s). Copyright © 2001 John Wiley & Sons, Ltd.

We isolated spontaneous mutants resistant to sodium orthovanadate in the biotechnologically significant yeast Kluyveromyces lactis . Resistance behaved as a recessive character in all mutants analyzed. Four genes were defined by complementation analysis, from vga1 to vga4 . These mutants showed defects in N-linked as well as O-linked glycosylation processes. In addition, the mutants exhibited sensitivity to the aminoglycoside hygromycin B and to calcofluor white, with the exception of vga4 ; this mutant grew in the presence of the antibiotic as well as the parental wild type and was resistant to calcofluor. The mutations were accompanied by alterations in the cell wall structure, as revealed by the delocalisation of chitin, changes in cell shape and size and by the clumpy aspect of the cultures. The mutants isolated provide basic tools for molecular and cellular analysis of glycosylation processes in K. lactis .