Sequence analysis of the upstream regions of Xenopus laevis beta-globin genes and arrangement of repetitive elements within the globin gene clusters.

The globin gene clusters of Xenopus laevis are interspersed by various different repetitive DNA elements. A specific repeat, the JH12 element, has been mapped by Southern analysis and some of its locations have been subsequently confirmed by nucleotide sequencing. JH12 family members seem to represent mobile genetic elements and display a high degree of divergence. The nucleotide sequences upstream to the adult beta I-globin gene and to the two coordinately expressed larval beta I- and beta II-globin genes have been determined and compared to those of the adult alpha-genes. Besides some repetitive DNA elements and a short sequence of rather weak homology we have found no characteristic sequence motifs to be common to the adult alpha- and beta-genes. The two larval beta-genes share one short sequence element being absent from the adult genes. This might reflect completely different sequence requirements for protein interactions and for the regulation of adult and larval globin gene expression.