Studies on the Role and Mode of Operation of the Very‐Lysine‐Rich Histone H1 in Eukaryote Chromatin

Abstract

Limited digestion with trypsin of both calf thymus H1 histone and the fragment 1 -120 of the H1 molecule has resulted in the isolation of the fragment 35-120. This fragment assumes a globular structure under physiological conditions of pH and ionic strength. The variable N-terminal portion of the molecule, up to residue 34, is not required for the formation of the HI globular structure.Proton nuclear magnetic resonance (NMR) and ultracentrifugation studies show that the H1 histone molecule consists of three distinct structural domains under structuring conditions : a random coil 'nose' consisting of 35 to 40 residues from the N-terminal end; a globular 'head' involving the next approximately 80 residues; and a random-coil 'tail' of the remainder of the molecule.The closely related class of basic eukaryotic chromosomal proteins, generically known as the very-lysine-rich or H1 histones, are quite distinct from the other histones on several counts. They are not, as are the other histones, required for the formation of the nucleosome substructure of the chromosome [l]. It is widely believed that they are involved in higher-order structures in the chromosome [2]. It is noteworthy that even in single tissues there are several subfractions of this protein, and that the relative proportions of the subfractions vary from tissue to tissue of the same species [3,4], implying that they are not functionally identical. Metabolic modification (phosphorylation) of the corresponding proteins in the synchronous slime mould Physarum polycephalum is associated with the initiation of mitotic chromosome condensation [5,6].In early sequence studies Bustin and Cole [7] recognised three distinct regions of the H1 molecule, based on amino acid composition. Firstly a region of about 40 residues starting from the N-terminus which is highly variable in sequence between subfractions. The next 80 residues are highly conserved and include nearly all of the hydrophobic residues in the molecule. The remainder of the molecule (about 95 residues) is highly basic, and contains repetitive sequences rich in lysine, alanine and proline.In a previous paper [8] it has been shown that part of the H1 molecule adopts a globular structure Abbreviations. NMR, proton nuclear magnetic resonance; dansyl, 5-dimethylaminonaphthalene-I-sulphonyl.under physiological conditions of ionic strength and pH. It has also been shown that the basic 'tail' of the molecule is not required for the formation of this structure, and that the C-terminal limit of the minimum globular structure is somewhere between residues 107 and 120 [8,9]. (The sequence numbering is based on alignment with the sequence of RTL3 H1, a subfraction from rabbit thymus gland, which has been published up to residue 107 [lo].) Additional sequence information has been made available to us (H. W. Hsiang and R. D. Cole, private communication). As a result of this numbering system the residue numbers may not be precisely correct for all subfractions owing to the possibility of insertions or deletions in the ...

Cell-cycle-dependent dissociation of histone H1 from chromatin in nuclei of P. polycephalum

“…This is supported by physical studies of Hi in solution [9]. The three domains are: the amino terminal segment (residues which is largely unstructured; the central structured region (residues which may -be folded into a specific tertiary structure [9,10], the highly basic carboxyl ter-minal half which appears to be in a random conformation. These three structural domains may be associated with three quite distinct functional roles in the various orders of folding of the basic nucleosome fibre.…”

The Structure of Sea‐Urchin‐Sperm Histone φ1 (H1) in Chromatin and in Free Solution

“…Earlier studies [6,7] of the structure of the peptides excised from histones H1 and H5 by trypsin digestion showed that they contained all the secondary and tertiary structure found in the intact parent molecule. The same finding is reported here for sea urchin sperm histone 41.…”

“…It has previously been demonstrated that both calf thymus histone H1 [6] and chicken erythrocyte H5 [7] consist of three structural domains in free solu- tion. Histone 41, although clearly an HI histone, shows very considerable compositional and sequence differences from calf thymus H1 and from chicken erythrocyte H5 [lo, 15,201.…”

“…A similar approach has been taken in the study of the conformation of histone H1 in free solution. Tryptic digestion was shown to result in preferential digestion of 35 N-terminal residues and all the C-terminal half of the molecule beyond residue 120 [6]. The remaining central portion of the molecule was shown to contain all the secondary and tertiary structure of intact H1 and moreover to retain this structure after removal of the N-terminal and C-terminal regions.…”

Phosphorylated sites of chicken erythrocyte histone H5 by a cyclic AMP‐independent protein kinase from mouse plasmocytoma cells

“…Even if the specificity is different from one kinase to another, the sites of phosphorylation in histone H5 are distributed in vitro as in vivo in two distinct regions of the protein: the amino-terminal region (residues 1-21) and the carboxy-terminal region (residues 101-189); in all cases, no site has been detected in the globular part of the molecule (residues 22-100) [9]. This fact has been already mentioned for histone H 1 which, like histone H5, conrains 3 different domains: a short apolar amino-terrninal part in random coil (residues 1-34); a globular central part (residues 35-120); and a highly basic carboxy-terminal part in random coil (residues 121-213) [10]. Phosphorylation of histone H1 by a cyclic AMPdependent protein kinase only takes place at serine residue 37 in the amino-terminal region of the molecule while phosphorylation by a cyclic AMP-independent protein kinase occurs at serine and threonine residues, mainly in the carboxy-terminal region.…”