Structure of Globin Gene Domains in Mammals and Birds

The data on the structure of gene domains of both mammalian and avian α- and β-globin genes are reviewed. The specific features of chromatin, DNA binding to the nuclear matrix, and domain-specific transcripts are discussed. In humans, the β-globin gene domain is located in the GC-depleted isochore and contains multiple nuclear matrix attachment regions. The locus is controlled by six chromatin DNase hypersensitive sites located far upstream of the first structural gene. Some of these regions display enhancer activity to support normal transcription level in the domain. Other mammalian β-globin domains are similarly organized. The avian β-globin genes are specifically arranged and their expression is less dependent from the locus control region. The human α-globin gene is located in the GC-rich isochore. The nuclear matrix attachment sites are not identified in this gene. An analog of the locus control region is located 40 kb upstream of the ζ-globin gene. The avian α-globin gene domains contain numerous nuclear matrix attachment regions. In these domains, an element located far upstream the genes regulates positive rather than negative transcription. An unidentified housekeeping gene as well as some other transcripts not encoding the structural globin genes is transcribed in the direction opposite to that of the globin genes in both mammalian and avian domains.