Abstract. The alphoid DNA.CENP-B (centromere protein B) complex is the first sequence-specific DNA/ protein complex detected in the centromeric region of human chromosomes. In the reaction, CENP-B recognizes a 17-bp sequence (CENP-B box) and assembles two alphoid DNA molecules into a complex, which is designated complex A (Muro, Y., H. Masumoto, K. Yoda, N. Nozaki, M. Ohashi, and T. Okazaki. 1992. J. Cell Biol. 116:585-596). Since CENP-B gene is conserved in mammalian species and CENP-B boxes are found also in mouse centromere satellite DNA (minor satellite), this sequence-specific DNAprotein interaction may be important for some kind of common centromere function. In this study we have characterized the structure of CENP-B and CENP-B.alphoid DNA complex. We have shown by chemical cross-linking that CENP-B formed a dimer, and have estimated by molecular weight determination the composition of complex A to be a CENP-B dimer and two molecules of alphoid DNA. The DNA binding domain has been delimited within the NH~-terminal 125-amino acid region containing four potential or-helices using truncated CENP-B made in Escherichia coli cells. We have shown that CENP-B had sites highly sensitive to proteases and that the DNA binding domain was separable from the dimerizing activity by the proteolytic cleavage at 20 kD from the COOH terminus of the molecule. Thus, CENP-B may organize a higher order structure in the centromere by juxtaposing two CENP-B boxes in the alphoid DNA repeat through both the DNA-protein and protein-protein interactions.

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Berberine sulfate, an isoquinoline alkaloid isolated from Hydrastis canadensis L., inhibited the effects of the tumor promoters 12–O-tetradecanoylphorbol-13-acetate and teleocidin, such as increased ³²P_i-incorporation into phospholipids of cell membrane and hexose transport. Berberine sulfate also markedly suppressed the promoting effect of teleocidin on skin tumor formation in mice initiated with 7,12-dimethyl-benz[a]anthracene.

Glycyrrhetic acid inhibited the action of tumor promoter in vitro and in vivo. Glycyrrhetic acid inhibited the increased phospholipid metabolism of cultured cells induced by tumor promoters, 12-O-tetradecanoylphorbol-13-acetate or teleocidin, and it markedly suppressed the promoting effect of teleocidin on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene.