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Nineteen open reading frames (ORFs) in the left arm of chromosome XI of the yeast Saccharomyces cerevisiae were inactivated. This was done by producing single-gene or contiguous-gene deletions in haploid and diploid strains. Four deletions are lethal to the corresponding haploid strains, and two result in a failure to grow on a rich glycerol medium. Complementation experiments showed that five of the six identified phenotypes were due to deletion of a single gene (ORFs YKL173w, YKL172w, YKL165c, YKL154w are essential, and YKL160w is required for growth on glycerol medium). One of the phenotypes observed on glycerol medium was not suppressed by the corresponding deleted genes. None of the other deletions, covering 13 ORFs in all, gave rise to any obvious phenotype when the cells were grown at three different temperatures on rich glycerol or glucose medium or on minimal synthetic medium.

In the frame of the European Network for Functional Analysis (EUROFAN), two regions from chromosome XI covering 54kb have been subjected to 'mass-murder'. Ten deletions covering 23 novel open reading frames (ORFs) were constructed in haploid and diploid strains. Six deletions were lethal in haploid strains. One deletion caused slow germination of spores and slow cellular growth, and another one was associated with both cellular growth thermosensitivity and poor growth on glycerol. These two defects were assigned to two different genes. All mutant phenotypes were complemented by a single gene, enabling us to identify five genes essential for vegetative growth, three genes with detectable phenotype and 15 dispensable genes under standard physiological conditions.

The complete sequence of the yeast Saccharomyces cerevisiae reveals the presence of many new genes, many of which are without homologs in databases. Characterisation of these genes by novel methods includes systematic deletion followed by phenotypic analysis of mutant strains. We have developed a hierarchical strategy for such a functional analysis of genes, in which the primary phenotypic screening is performed on groups of contiguous genes which are then reinvestigated down to the single gene level. This strategy is applied to the whole chromosome XI as part of EUROFAN (the EUROpean Functional ANalysis) program, and we present here our results on a group of 22 genes from this chromosome. This sample is representative of the results that are emerging for the whole chromosome. Out of the 22 genes deleted, three were shown to be essential, and another three genes confer a mutant growth phenotype to cells when deleted. All phenotypes have been complemented. These figures are in accordance with the previously published fraction of lethal and growth-defective deletions of single genes. We have found no synthetic phenotypes resulting from a combination of deleted genes and have always been able to attribute a mutant phenotype to a single gene.