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Abstract

The centromere/kinetochore complex is indispensable for accurate segregation of chromosomes during cell divisions when it serves as the attachment site for spindle microtubules. Centromere identity in metazoans is believed to be governed by epigenetic mechanisms, because the highly repetitive centromeric DNA is neither sufficient nor required for specifying the assembly site of the kinetochore 1, 2, 3 and 4. A candidate for an epigenetic mark is the centromere-specific histone H3 variant CENP-A that replaces H3 in alternating blocks of chromatin exclusively in active centromeres 1, 2, 5 and 6. CENP-A acts as an initiator of kinetochore assembly, but the detailed dynamics of the deposition of metazoan CENP-A and of other constitutive kinetochore components are largely unknown 1, 2, 7, 8, 9 and 10. Here we show by quantitative fluorescence measurements in living early embryos that functional fluorescent fusion proteins of the Drosophila CENP-A and CENP-C homologs are rapidly incorporated into centromeres during anaphase. This incorporation is independent of ongoing DNA synthesis and pulling forces generated by the mitotic spindle, but strictly coupled to mitotic progression. Thus, our findings uncover a strikingly dynamic behavior of centromere components in anaphase.