Deletion of a particular gene is often the first step to working out its function. In the 25 July Nature, Guri Glaever and colleagues report the creation of a nearly complete collection of gene-deletion mutants (representing 96% of all annotated ORFs) of the yeast Saccharomycescerevisiae (Nature 2002, 418:387-391).

Glaever et al. deleted each gene, from start to stop codon, by replacing it with a deletion cassette incorporating the KanMX gene flanked by two distinct 20-nucleotide sequences that serve as unique 'molecular bar codes' for identification. They deleted 5,916 genes in this manner, 18.7% of which proved to be essential for growth on glucose-rich medium. The unique sequence tags allow strains to be analyzed in parallel. Mixed cultures can be grown and sampled and the abundance of each deletion strain determined by hybridization of genomic DNA to an oligonucleotide microarray of the complementary bar-code sequences.

Using...