The expression of human H2A-H2B histone gene pairs is regulated by multiple sequence elements in their joint promoters

The majority of human H2A and H2B histone genes are organized as gene pairs : 14 H2A-H2B gene pairs, one solitary H2A gene and three solitary H2B genes have been described. Two of the H2A genes and two of the H2B genes arrange d within gene pairs are pseudogenes. The gene pairs are organized with dive rgent transcriptional orientation, and the coding regions of the respective H2A and H2B genes are separated by about 320 nucleotide pairs that form ov erlapping promoter regions. Comparison of promoters of H2A-H2B gene pairs h as previously shown that these belong to two different groups (groups I and II) which are characterized by specific patterns of conserved sequence ele ments. We have constructed a reporter gene vector that allows the simultane ous analysis of both genes regulated by the divergent promoters belonging t o group I or II, respectively. Firefly-luciferase and P-galactosidase genes were taken as reporter genes. Site directed mutagenesis performed at indiv idual promoter elements revealed that individual sequence elements within b oth groups of promoters functionally depend on each other and may contribut e to a coordinate expression of paired H2A and H2B genes through assembly o f their joint promoter into a mutually dependent promoter complex. Group II promoters are characterized by the presence of an E2F binding site upstrea m of the H2A gene-proximal TATA box. Immediately upstream of the E2F elemen t, we have identified a highly conserved octanucleotide CACAGCTT (RT-1) tha t exists in all human group II H2A-H2B gene promoters. Protein binding stud ies at the RT-1 element indicate factor binding to this sequence. Site dire cted mutagenesis indicates that both the E2F element and the RT-1 motif are essential for full promoter activity. (C) 1999 Elsevier Science B.V. All r ights reserved.