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Thermal denaturation of nucleohistones—effects of formaldehyde reaction
Author(s) -
Li Hsueh Jei
Publication year - 1972
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1972.360110408
Subject(s) - chemistry , formaldehyde , dna , denaturation (fissile materials) , nucleoprotein , histone , nucleic acid denaturation , covalent bond , crystallography , molecule , helix (gastropod) , biophysics , biochemistry , organic chemistry , nuclear chemistry , ecology , biology , snail , base sequence
Thermal denaturation of native or partially dehistonized nucleohistones shows two melting bands at 66 and 81° in 2.5 × 10 −4 M EDTA, pH 8.0. These correspond to the melting of DNA segments bound by the less basic and the more basic half‐molecules of histones, respectively. These two melting bands combine into a broad melting band from around 70 to 85° when these nucleohistones are pre‐treated with formaldehyde. A formaldehyde reaction which fixes histones on DNA by covalent bonds account for the effect. Formaldehyde fixation also increases the melting temperature of some free DNA segments from around 42 to around 55°. This is interpreted as a result of closed or rigid boundaries between free DNA and formaldehyde‐reacted histone‐bound DNA segments. MgCl 2 dissociates histones from DNA more effectively and leaves longer free DNA segments than does NaCl. Thermal denaturation of a formaldehyde‐reacted nucleoprotein thus provides an effective tool for comparing the relative size of free DNA regions on nucleoproteins. The effect of reversible binding of ligands on helix‐coil transition of DNA is descussed and found not adequate for thermal denaturation of nucleohistones.