Identification of a 34 amino acid stretch within the C-terminus of histone H1 as the DNA-condensing domain by site-directed mutagenesis

Biochemistry. 2002 Jun 18;41(24):7617-27. doi: 10.1021/bi025773+.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acids / chemistry*
  • Amino Acids / genetics*
  • Animals
  • DNA / metabolism*
  • DNA Mutational Analysis
  • Histones / chemistry*
  • Histones / genetics*
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed*
  • Oligopeptides / chemistry
  • Oligopeptides / genetics
  • Peptide Fragments / chemistry*
  • Peptide Fragments / genetics*
  • Point Mutation
  • Protein Structure, Secondary / genetics
  • Protein Structure, Tertiary / genetics
  • Rats
  • Repetitive Sequences, Amino Acid
  • Sequence Deletion

Substances

  • Amino Acids
  • Histones
  • Oligopeptides
  • Peptide Fragments
  • DNA