YY1 binding sites within the ORFs of the olfactory receptor and histone 4 gene families. Four examples of olfactory receptor genes and histone 4 genes are shown with the location and direction of their YY1 binding sites. Large gray boxes indicate open reading frames (ORFs) of these single exon genes. Boxes above each ORF show forward direction (empty box) and reverse direction (filled box) of the YY1 binding sites. The arrows in each ORF represent transcriptional directions. The bottom plot shows amino acid sequence identity for all members of each family. A total of 1,178 olfactory receptor proteins have 35% sequence identity (the four shown have 52%) while six genes of the histone 4 family share 95% identity. Conservation of position of YY1 binding sites is non-existent in olfactory genes while it is perfectly preserved in the histone 4 gene family. Directional bias in olfactory genes reflected in the figure is consistent with the complete dataset which yields 3.4 forward sites for every reverse site per 1 kb. The dipeptides encoded by the core motif of the YY1 binding site are identical for all six homologs of the histone 4 gene family (four shown). Olfactory receptor genes, by contrast, have a high number of YY1 binding sites that do not correlate to the position of these dipeptides.