CARBOXYL-TERMINAL PEPTIDES FROM HISTONE H1 VARIANTS - DNA-BINDING CHARACTERISTICS AND SOLUTION CONFORMATION

The carboxyl-terminal domains of the histone HI proteins bind to DNA a nd are important in condensation of DNA. Little is known about the det ails of the interactions between HI histones and DNA, and in particula r, there is little known about differences among variant HI histones i n their interactions with DNA. Questions concerning HI histone-DNA aff inity and HI conformation were investigated wing peptide fragments fro m the carboxyl terminal domains of four nonallelic histone HI variant proteins (mouse H1-1, H1-4 and H1 degrees, and rat Hit). Three of the Sour peptides showed a slight preferencefor binding to a GC-rich regio n of a 214-base-pair DNA fragment, rather than to an AT-rich region. T he fourth peptide, Hit, appeared to bind preferentially to the A T-ric h region of the 214-base-pair fragment. The results show that these sm all peptides bind preferentially to a subset of DNA sequences; such se quence preference might be exhibited by the intact HI histones themsel ves. CD spectra of the peptides, which are from regions of the protein s that are not compactly folded, showed that the alpha-helical content of the peptides was minimal if the peptides were in 10 mM phosphate b uffer; brit increased if the peptides were in 1M NaClO4 and 50% triflu oroethanol, conditions that are postulated to approximate certain aspe cts of binding to DNA. H1-4 peptide, which was predicted to be 70% alp ha-helix, but was not cy-helical in IO mM phosphate buffer, appeared f rom difference CD spectra to be more alpha-helical when it was bound t o DNA. The regions of the proteins from which these peptides are deriv ed, which are extended in solution, may fold, forming alpha-helices, r ipen binding to DNA. (C) 1996 John Wiley & Sons, Inc.