Phosphorylation of the CENP-A amino-terminus in mitotic centromeric chromatin is required for kinetochore function

Abstract

The role of the mitotic phosphorylation of the amino (NH2) terminus of Centromere Protein A (CENP-A), the histone variant epigenetic centromeric marker, remains elusive. Here, we show that the NH2 terminus of human CENP-A is essential for mitotic progression and that localization of CENP-C, another key centromeric protein, requires only phosphorylation of the CENP-A NH2 terminus, and is independent of the CENP-A NH2 terminus length and amino acid sequence. Mitotic CENP-A nucleosomal complexes contain CENP-C and phosphobinding 14-3-3 proteins. In contrast, mitotic nucleosomal complexes carrying nonphosphorylatable CENP-A-S7A contained only low levels of CENP-C and no detectable 14-3-3 proteins. Direct interactions between the phosphorylated form of CENP-A and 14-3-3 proteins as well as between 14-3-3 proteins and CENP-C were demonstrated. Taken together, our results reveal that 14-3-3 proteins could act as specific mitotic "bridges," linking phosphorylated CENP-A and CENP-C, which are necessary for the platform function of CENP-A centromeric chromatin in the assembly and maintenance of active kinetochores.