Homeodomain protein binding sites, inverted repeats, and nuclear matrix attachment regions along the human...

beta-Globin genes in primates arose during evolution by duplication of an ancestral gene, and their order of arrangement along the DNA is related to their timing of expression during development. We believe that nuclear matrix anchorage sites (MARs) along the beta-globin gene complex considered to be mass binding sites for transcription protein factors, some of which are developmental stage specific and others ubiquitous, play a decisive role in cell memory by determining the developmental stage-specific expression of the genes. The AT-rich class of MARs appears to possess a significant number of ATTA and ATTTA motifs known to be mass binding sites for homeodomain proteins that determine body formation in development. MARs also appear to harbor origins of replication, to be enriched in inverted repeats (dyad symmetry motifs) and were proposed to include the DNase I hypersensitive sites of a particular gene determined at the chromatin level. This study is an attempt to finely identify MARs at the nucleotide level along the beta-globin gene complex. Searches of a contiguous stretch of about 73.3 kb of human sequences comprising and surrounding the epsilon, gamma G-, gamma A-, delta-, and beta-globin genes of the human beta-globin gene complex for homeotic protein binding sites as well as for inverted repeats has shown that these elements are clustered nonrandomly at particular sites within the beta-globin gene complex. These sites are presumed to be the AT-rich class of MARs of the beta-globin gene complex. The inverted repeats which are characteristic of origins of replication and some promoter/enhancer regions and the homeotic protein sites seem to include the DNase I hypersensitive sites of the gene complex. Indeed, dyad symmetry sequences are present close to the four DNase I HS sites in the locus control region (LCR) of the gene complex as well as in the 5' flanking regions and the large introns of the delta- and beta-globin genes. A search of the putative MAR regions of the gene complex suggests that, in addition to their enrichment in ATTA motifs, palindromes, and DNase I hypersensitive sites, these regions may comprise TG-rich motifs and potential Z-DNA as well as polypurine and polypyrimidine blocks. From the positions of palindromes and clusters of homeodomain protein sites along the complex we propose that an extended origin of replication able to initiate at several sites is present in the LCR and two others surrounding the delta- and beta-globin genes.(ABSTRACT TRUNCATED AT 400 WORDS)