title: Identification of a 34 amino acid stretch within the C-terminus of histone H1 as the DNA-condensing domain by site-directed mutagenesis.
abstract: The C-terminus of histone H1 is necessary for the folding of polynucleosomal arrays into higher-order structure(s) and contains octapeptide repeats each having DNA binding S/TPKK motifs. These repeat motifs were earlier shown to mimic the DNA/chromatin-condensing properties of the C-terminus of histone H1 (Khadake, J. R., and Rao, M. R. S. (1995) Biochemistry 36, 1041-1051). In the present study, we have generated a series of C-terminal mutants of rat histone H1d and studied their DNA-condensation properties. The single proline to alanine mutation in the S/TPKK motifs either singly or in combination resulted in only a 20% decrease in the DNA-condensation property of histone H1. Deletion of all the three S/TPKK motifs resulted in a 45% decrease in DNA condensation. When the three octapeptide repeats encompassing the S/TPKK motifs were deleted, there was again a 45% decrease in DNA condensation. On the other hand, when the entire 34 amino acid stretch (residue 145-178) was deleted, there was nearly a 90% decrease in DNA condensation brought about by histone H1d. Interestingly, deletion of the 10 amino acid spacer between the octapeptide repeats (residues 161-170) also reduced the DNA condensation by 70%. Deletion of the region (residues 115-141) immediately before the 34 amino acid stretch and after the globular domain and the region (residues 184-218) immediately after the 34 amino acid stretch had only a marginal effect on DNA condensation. The importance of the 34 amino acid stretch, including the 10 amino acid spacer, was also demonstrated with the recombinant histone H1d C-terminus. We have also determined the induced alpha-helicity of histone H1 and its various mutants in the presence of 60% trifluoroethanol, and the experimentally determined induced helical contents agree with the theoretical predictions of secondary structural elements in the C-terminus of histone H1d. Thus, we have identified a 34 amino acid stretch in the C-terminus of histone H1d as the DNA-condensing domain.
authors.affiliation: Department of Biochemistry and Bioinformatics Centre, Indian Institute of Science, Bangalore 560012, India.
authors.forename: M M Srinivas
authors.initials: MM
authors.lastname: Bharath
authors.forename: Sneha
authors.initials: S
authors.lastname: Ramesh
authors.forename: Nagasuma R
authors.initials: NR
authors.lastname: Chandra
authors.forename: M R S
authors.initials: MR
authors.lastname: Rao
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry* / Q000235:genetics*; D000818:Animals; D004247:DNA / Q000378:metabolism*; D004252:DNA Mutational Analysis; D006657:Histones / Q000737:chemistry* / Q000235:genetics*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009842:Oligopeptides / Q000737:chemistry / Q000235:genetics; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics*; D017354:Point Mutation; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D051381:Rats; D020449:Repetitive Sequences, Amino Acid; D017384:Sequence Deletion
chemical_list: D000596:Amino Acids; D006657:Histones; D009842:Oligopeptides; D010446:Peptide Fragments; D004247:DNA