Fig. 1

Centromeric DNA sequences are not conserved through species. With the exception of S. cerevisiae, most evidence shows that DNA sequence has no role in centromere identity. Species comparison reveals vast differences in nucleotide composition as well as the centromere length. S. cerevisiae has a 125-bp centromere which is divided in three centromere DNA elements (CDE), with CDEII being the sequence important for Cse4 incorporation. It is still somewhat controversial whether this centromere is composed of a single or two to three CENP-A nucleosomes.(Lawrimore et al. 2011; Furuyama and Biggins 2007) S. pombe 10 kbp centromere consists of inner and outer repeats located outside the core region and in a head-to-head orientation. D. melanogaster has relatively large centromeres made up of DNA repeats and transposon elements for a genomic size of ∼420 kbp. A. thaliana and Homo sapiens centromeres are made of head-to-tail 171–178 bp repeats that can go up to 1.4 Mbp for the plant and 5 Mbp for human. General centromere structures display two general types of centromere: monocentric for S. cerevisiae to H. sapiens, and holocentric (whole length of chromosome) for C. elegans (generally nematodes and several other species) (Maddox et al. 2004; Melters et al. 2012) Elongated centromeric chromatin may have different arrangements of CENP-A and H3 nucleosomes arrays, which are repetitive and exclusive from one another (Blower et al. 2002). When compacted, the CENP-A arrays form a hypothetical centromeric plate required for kinetochore formation in mitosis. Green circles H3 nucleosome, red circles CENP-A nucleosome