Histone H1

Linker histones of which histone H1 is a representative are a diverse family of architectural proteins within the eukaryotic nucleus. These proteins have a variety of structures, but invariably contain a region enriched in lysine, serine, alanine and profine. All metazoan histone His also include a structured domain that binds to DNA through a helix-turn-helix motif. By binding to the linker DNA flanking the nucleosome core they contribute to the assembly of higher-order chromatin structures. Surprisingly, the use of “knockout” technology to eliminate histone H1 in isolated cells and Xenopus does not prevent the assembly of chromosomes or nuclei, however specific genes are activated or repressed indicative of targeted regulatory functions. A dual role for histone HI in chromatin structure and gene regulation might contribute to epigenetic phenomena in which heritable states of gene activity are maintained through mechanisms independent of gene sequence. This may have important implications for biotechnological and medical research.