CENP-A is an essential histone H3 variant found in all eukaryotes examined to date. To begin to determine how CENP-A is assembled into chromatin, we developed a binding assay using sperm chromatin in cell-free extract derived from Xenopus eggs. Our data suggest that the catalytic activities of an unidentified deoxycytidine deaminase and UNG2, a uracil DNA glycosylase, are involved in CENP-A assembly. In support of this model, inhibiting deoxycytidine deaminase with zebularine, or uracil DNA glycosylase with Ugi, uracil or UTP results in a lack of detectable CENP-A on sperm DNA. Conversely, inducing DNA damage increases the level of CENP-A detected on sperm chromatin. Our data suggest that base excision repair may be involved in assembly of this histone H3 variant
