Comparative genome analysis delimits a chromosomal domain and identifies key regulatory elements in the α globin cluster

We have cloned, sequenced and annotated segments of DNA spanning the mouse, chicken and pufferfish a globin gene clusters and compared them with the corresponding region in man. This has defined a small segment (∼135-155 kb) of synteny and conserved gene order, which may contain all of the elements required to fully regulate a globin gene expression from its natural chromosomal environment. Comparing human and mouse sequences using previously described methods failed to identify the known regulatory elements. However, refining these methods by ranking identity scores of noncoding sequences, we found conserved sequences including the previously characterized a globin major regulatory element. In chicken and pufferfish, regions that may correspond to this element were found by analysing the distribution of transcription factor binding sites. Regions identified in this way act as strong enhancer elements in expression assays. In addition to delimiting the a globin chromosomal domain, this study has enabled us to develop a more sensitive and accurate routine for identifying regulatory elements in the human genome.