Many library mutants contain a deletion of an open reading frame (ORF) that also deletes part or all of an overlapping ORF. (A-D) Illustrations depicting overlapping genes found at four chromosomal loci. (E) ORFs whose coding regions were precisely deleted in the library strains and overlapping ORFs affected by the deletion. Genes listed as “verified” are known to produce a protein product (source: Saccharomyces Genome Database). All other ORFs are unverified.