All S. cerevisiae ORFs are designated by a symbol consisting of three uppercase letters followed by a number and then another letter, as follows: Y (for "Yeast"); A - P for the chromosome upon which the ORF resides (where "A" is chromosome I, up to "P" for chromosome XVI); L or R (for Left or Right arm); a 3-digit number corresponding to the order of the open reading frame on the chromosome arm (starting from the centromere and counting out to the telomere); and W or C for whether the open reading frame is on the "Watson" or "Crick" strand (where "Watson" runs 5' to 3' from left telomere to right telomere). Most ORF designations by the systematic sequencing groups use a predicted 100 amino acid polypeptide as the minimum size limit, except when a smaller gene has already been characterized and localized to the chromosomal sequence. When a new ORF is discovered on a chromosome that has already had its ORF's named, the new ORF will usually be named by taking the name of an adjacent ORF and adding an "A" or "B" to the end of it (this avoids re-numbering all the distal ORF's).

This definition is in context to Yeast Genome. See more contextual defintions for ORF naming conventions.