Fig. 2. CENP-B and CENP-C bind the alpha-satellite DNA of different human chromosomes and recognize the same subfamilies of DNA sequences. (A) Filters were prepared as described in Fig. 1A and sequentially hybridized with alpha satellite probes recognizing, at high stringency, only a subset of human centromeric sequences. The specific chromosomes recognized by each probe are indicated. PI serum (pre-immune serum), anti-CENP-B and anti-CENP-C indicate the DNA recovered with the corresponding antibodies. (B) HeLa cells were formaldehyde-treated and chromatin was immunoprecipitated with the different sera. After reversal of crosslinking, DNA was digested with EcoRI, run on a 1.5% agarose gel and then blotted onto nylon membrane. Alpha-satellite DNA was revealed by hybridizing the filter with probes specific for alpha-satellite of chromosomes 7, 13 and 21. Dimers, tetramers and pentamers are multimers of the 171 bp alpha-satellite monomeric unit.