UASt regulatory sequences are fused upstream of two open reading frames separated by stop codons (the upstream ORF is simply present to reduce translation of the downstream ORF). The downstream ORF encodes the chromodomain of Hsap\CBX7 (amino acids 7-61), which recognizes and binds H3K27me3 (His3 triply methylated at position K27), tagged at the C-terminal end with 2xTag:NLS(SV40-largeT) and with Tag:Dam (an intron has been introduced into the Tag:Dam coding sequence, which greatly improves cloning efficiency by preventing toxicity in bacteria).