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Abstract
The lysine-rich H1 histone family in mammals includes eleven different subtypes, and
thus it is the most divergent class of histone proteins. The central globular H1 domain
asymmetrically interacts with DNA at the exit or entry end of the nucleosomal core
DNA, and the C-terminal domain has a major impact on the linker DNA conformation and
chromatin condensation. H1 histones are thus involved in the formation of higher order
chromatin structures, and they modulate the accessibility of regulatory proteins,
chromatin remodeling factors and histone modification enzymes to their target sites.
The major posttranslational modification of H1 histones is phosphorylation, which
reaches a peak during G2 and mitosis. Phosphorylation is, however, also involved in
the control of DNA replication and it contributes to the regulation of gene expression.
Disruption of linker histone genes, initially performed in order to delineate subtype-specific
functions, revealed that disruption of one or two H1 subtype genes is quantitatively
compensated by an increased expression of other subtypes. This suggests a functional
redundancy among H1 subtypes. However, the inactivation of three subtypes and the
reduction of the H1 moiety in half finally resulted in a phenotypic effect. On the
other hand, studies on the role of particular subtypes at specific developmental stages
in lower eukaryotes, but also in vertebrates suggest that specific subtypes of H1
participate in particular systems of gene regulation.