Species-specific suppression of histone H1 and H2B production in human/mouse hybrids.

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Abstract
Ten human/mouse hybrid cell lines that segregate either human or mouse chromosomes were examined for the expression of human- and mouse-specific histones H1 and H2B. The human and mouse chromosomes in hybrid cells that segregate human chromosomes (M > H hybrids) contain only mouse histones H1 and H2B. Chromosomes in hybrid cells that segregate mouse chromosomes (H > M hybrids) contain only human H1 and H2B histones. Loss of the ability to produce either human or mouse histones apparently is not due to the loss of specific human or mouse chromosomes because M > H hybrids retaining at least 1 copy of each human chromosome contain only mouse H1 and H2B and H > M hybrids retaining at least 1 copy of each mouse chromosome contain only human H1 and H2B histones. The control mechanisms affecting H1 and H2B expression in H > M and in M > H hybrid cells apparently affect expression of histones H2A, H3, and H4 genes as evidenced by H4 acetylation levels and similarities in the ratios of H3 and H2A histone variants between parents and offspring. The hypothesis that none of the histone genes that are active in the recessive parent cell type are expressed in hybrid lines that segregate recessive cell chromosomes is supported.