Functional analysis of 12 ORFs from Saccharomyces cerevisiae chromosome II

Automated screening in environmental arrays allows analysis of quantitative phenotypic profiles in Saccharomyces cerevisiae

A methodology for large-scale automated phenotypic profiling utilizing quantitative changes in yeast growth has been tested and applied to the analysis of some commonly used laboratory strains. This yeast-adjusted methodology is based on microcultivation in 350 microl liquid medium, where growth is frequently optically recorded, followed by automated extraction of relevant variables from obtained growth curves. We report that cultivation at this micro-scale displayed overall growth features and protein expression pattern highly similar to growth in well aerated medium-scale (10 ml) culture. However, differences were also encountered, mainly relating to the respiratory potential and the production of stress-induced proteins. Quantitative phenotypic profiles for the laboratory yeast strains W303, FY1679 and CEN-PK.2 were screened for in environmental arrays, including 98 different conditions composed of low, medium and high concentrations of 33 growth inhibitors. We introduce the concepts phenotypic index(rate) and phenotypic index(stationary), which relate to changes in rate of growth and the stationary phase optical density increment, respectively, in a particular environment relative a reference strain. The laboratory strains presented selective phenotypic profiles in both phenotypic indexes and the two features appeared in many cases to be independent characteristics. We propose the utilization of this methodology in large-scale screening of the complete collection of yeast deletion mutants.

Functional analysis of yeast gene families involved in metabolism of vitamins B1and B6

In order to clarify their physiological functions, we have undertaken a characterization of the three-membered gene families SNZ1-3 and SNO1-3. In media lacking vitamin B(6), SNZ1 and SNO1 were both required for growth in certain conditions, but neither SNZ2, SNZ3, SNO2 nor SNO3 were required. Copies 2 and 3 of the gene products have, in spite of their extremely close sequence similarity, slightly different functions in the cell. We have also found that copies 2 and 3 are activated by the lack of thiamine and that the Snz proteins physically interact with the thiamine biosynthesis Thi5 protein family. Whereas copy 1 is required for conditions in which B(6) is essential for growth, copies 2 and 3 seem more related with B(1) biosynthesis during the exponential phase.

Identification and characterization of Saccharomyces cerevisiae mutants defective in fluid-phase endocytosis

A mutant library generated by the European Functional Analysis Network (EUROFAN) was screened for strains defective in fluid-phase endocytosis. Accumulation of Lucifer yellow in the vacuole was used as a marker for efficient endocytosis. Fourteen mutants, including ede1Delta, rcy1Delta, sys1Delta and tlg2Delta, previously described to be involved in membrane trafficking, were identified in this screen. alpha-Factor uptake, endocytosis of FM4-64, carboxypeptidase Y secretion, vacuolar morphology, and a vma2 synthetic growth defect were used as criteria to characterize the endocytic defect of the mutant strains obtained. Accordingly, eight mutant strains have endocytic phenotypes in addition to their defect in Lucifer yellow accumulation. These fluid-phase endocytosis mutants are defective at different steps of the endocytic pathway. Interestingly, only two mutants were defective for internalization, two for vacuolar protein sorting and four mutants had aberrant vacuolar morphologies. Some of the mutants identified in this screen that sort carboxypeptidase Y correctly may affect endocytosis at an early post-internalization step before the intersection of the endocytic with the vacuolar protein-sorting pathway.