Institut für Biochemie und Molekulare Zellbiologie, Georg-August-Universität Göttingen, Germany.
A solitary histone H3 gene encoding a novel H3 protein sequence has been isolated. This H3 gene maps to chromosome 1 (1q42), whereas we have shown previously that the majority of the human histone genes form a large cluster on chromosome 6 (6p21.3). In addition, a small cluster has been described at 1q21. The clustered histone genes are expressed during the S-phase of the cell cycle, hence their definition as replication-dependent histone genes. In contrast, expression of replacement histone genes is essentially cell-cycle independent; they are solitary genes and map outside the major clusters. The newly described H3 gene maps outside all known histone gene clusters and varies by four amino acid residues from the consensus mammalian H3 structure. In contrast to other solitary histone genes, this human H3 gene shows the consensus promoter and 3' flanking portions that are typical for replication-dependent genes.