Abstract
The histone and nonhistone proteins associated with interphase and metaphase chromosomes of HeLa cells have been compared. Chromatographic and disc electrophoretic studies establish that interphase and metaphase histones are similar. Metaphase chromosomes may be marginally richer in arginine-rich histones and poorer in lysine-rich histones than the interphase chromosomes. Histone III, which contains cysteine residues, occurs mainly in the reduced, monomeric form in interphase chromosomes. In metaphase chromosomes, these sulfhydryl groups are oxidized and histone III is either polymerized or complexed with acid-soluble nonhistone proteins through interpolypeptide disulfide bonds. Metaphase chromosomes contain acid-soluble proteins which are absent from interphase chromosomes. All of the additional acid-soluble proteins of metaphase chromosomes are shown to be nonhistones and it is concluded that the histone:DNA ratio is identical in interphase and metaphase chromosomes. The bulk of the acid-soluble nonhistone proteins of metaphase chromosomes was found to be polymerized through disulfide bridges; corresponding interphase nonhistone proteins display no evidence of similar polymerization. These facts may be related to the condensed state and metabolic inactivity of metaphase chromosomes.
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