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. Author manuscript; available in PMC: 2019 Sep 1.
Published in final edited form as: Chromosome Res. 2018 Jul 5;26(3):115–138. doi: 10.1007/s10577-018-9582-3

Figure 4. Distribution of CENP-B boxes within different types of alpha satellite HORS.

Figure 4.

a) Not all alpha satellite monomers contain the 17-bp binding motif of the centromere protein CENP-B. Some HORs, like D7Z1, have a regular, alternating pattern of CENP-B boxes, so that reiteration of the HOR unit yields a large array with dense numbers of CENP-B boxes (monomers with white circles).

b) Pentameric SF3 arrays, like that of D11Z1 (cenll.l), DXZ1 (cenX.l), and the smaller array of D17Z1-B (cenl7.2), have the same number of CENP-B boxes, or more, as the dimeric arrays, but the CENP-B boxes are irregularly spaced. These arrays with irregularly spaced CENP-B boxes are equally competent for centromere assembly.

c) Some HOR arrays, like that of D7Z2 (cen7.2, SF5) have few or no CENP-B boxes and were thought to be “dead arrays” that lack centromere potential. However, D7Z2 (cen7.2) that only has one CENP-B box in monomer 16 can recruit centromere proteins (Thakur and Henikoff, 2018) and assemble a functional centromere (Hayden et al., 2013, McNulty et al., 2017).