The chicken CR1 subfamilies have a distinct 5'UTR sequences. (A) Diagram of the approximately 4.5 kb full-length chicken CR1 element structure. The 5'UTR promoter region analysed is boxed. (B) The 5'UTR of CR1-B subfamily contains sequences similar to those found in the sequence from turtle, pufferfish and other reptiles CR1 elements. E boxes and other binding sites for transcription factors found in this region are shown in shaded regions. The putative transcriptional start codon is highlighted in green. (C) The 5'UTR sequences of the CR1-F subfamily. The shaded regions show the binding sites for several transcriptional factors including Oct-1 and RXR-β sites.