Identification of a 34 Amino Acid Stretch within the C-Terminus of Histone H1 As the DNA-Condensing Domain by Site-Directed Mutagenesis

• Published in: Biochemistry (Easton) Vol. 41; no. 24; pp. 7617 - 7627
• Main Authors: Bharath, M. M. Srinivas, Ramesh, Sneha, Chandra, Nagasuma R, Rao, M. R. S
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 18.06.2002
• Subjects: 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
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi025773+

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 α-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.