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

Bharath, Srinivas MM and Ramesh, Sneha and Chandra, Nagasuma R and Rao, MRS (2002) Identification of a 34 Amino Acid Stretch within the C-Terminus of Histone H1 As the DNA-Condensing Domain by Site-Directed Mutagenesis. In: Biochemistry, 41 (24). 7617 -7627.

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Official URL: http://pubs.acs.org/doi/abs/10.1021/bi025773%2B

## 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.

Item Type: Journal Article Copyright of this article belongs to American Chemical Society. Division of Information Sciences > BioInformatics CentreDivision of Biological Sciences > Biochemistry 03 Jul 2007 18 Jan 2012 09:49 http://eprints.iisc.ernet.in/id/eprint/11364