FURTHER EVIDENCE THAT CENP-C IS A NECESSARY COMPONENT OF ACTIVE CENTROMERES - STUDIES OF A DIC(X-15) WITH SIMULTANEOUS IMMUNOFLUORESCENCE AND FISH

The stability of certain dicentric chromosomes in humans seems to resu lt from inactivation of one centromere, yielding a functionally monoce ntric chromosome. Centromere protein C (CENP-C) was previously shown t o be present at active centromeres but absent from the inactive centro mere of one homologous dicentric rearrangement. We have combined indir ect immunofluorescence detection of CENP-C and fluorescence in situ hy bridization with chromosome-specific alpha-satellite DNA probes in a s imultaneous assay to unequivocally identify the active and inactive ce ntromeres of a dicentric (X;15) translocation. In both fibroblast and lymphoblast cell lines containing the translocation, the X chromosome centromere consistently had a primary constriction and CENP-C immunofl uorescence, and is therefore the active centromere. CENP-C was never d etected at the chromosome 15 centromere, which appears to be inactive. The inactivation pattern is apparently stable and observed in all cel ls with the translocation. Immunofluorescence with CREST serum reveale d staining at both centromeres of the translocation, and thus was not specific to the active centromere. This study demonstrates the specifi city of CENP-C to the active centromere in a non-homologous rearrangem ent and further establishes CENP-C as an essential component of a func tional human centromere.