YY1 DNA-binding motifs as translated dipeptides. The four base pair core motif of the YY1 binding site is CCAT (forward) and ATGG (reverse). In principle, this core can code for two codons in each of the three frames. In the forward direction, CCAT can encode 29 possible dipeptides while in the reverse direction ATGG can encode 21 dipeptides, with one duplicate. These 49 dipeptides are a subset of the 400 possible dipeptides which can be found in a protein (20 total amino acids)2. The distribution frequency of these dipeptides has been examined to determine if any of the 49 YY1 binding sites is overrepresented in olfactory receptor genes.