Histone H1

Histone H1 is a group of one of the most well studied histone variants till date. They are about 21 to 29 kDa proteins consisting of 194-255 amino acid residues depending on the variant. H1 is a linker histone which binds to the 'nucleosome' from outside and facilitates further compaction of chromatin. Based on this function, these variants are recently classified into strong, intermediate and weak condensers of chromatin. The Histone H1 family contains 126 different members reported from diverse species. There are about 10 variants of histone H1 reported in humans. Unlike core histones (H2A, H2B, H3 and H4) which are often coded by multiple, non-allelic genes; H1 histones are coded by single gene each. Six of these genes are present on cluster 1 and the rest four are not in cluster. Except H1t all genes in cluster 1 show a replication dependent expression whereas the other members show a replication independent expression. Many variants of H1 follow a cell type/tissue specific expression pattern where they are involved in specific functions like replacement of histones with protamines in sperms to facilitate greater compaction of sperm chromatin.

Cytogenetic map of histone H1 coding genes
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Variants of histone H1
Variant (UniprotKB recommended name) UniprotKB Accession No. of coding gene(s)
Histone H1.0P073051 (H1F0)
Histone H1.1Q025391 (HIST1H1A)
Histone H1.2P164031 (HIST1H1C)
Histone H1.3P164021 (HIST1H1D)
Histone H1.4P104121 (HIST1H1E)
Histone H1.5P164011 (HIST1H1B)
Histone H1ooQ8IZA31 (H1FOO)
Histone H1tP224921 (HIST1H1T)
Histone H1xQ925221 (H1FX)
Testis-specific H1 histoneQ75WM61 (H1FNT)