Centromeric protein that plays a central role in the incorporation and maintenance of histone H3-like variant CENPA at centromeres. Acts as a specific chaperone for CENPA and is required for the incorporation of newly synthesized CENPA molecules into nucleosomes at replicated centromeres. Prevents CENPA-H4 tetramerization and prevents premature DNA binding by the CENPA-H4 tetramer. Directly binds Holliday junctions. {ECO:0000269|PubMed:19410544, ECO:0000269|PubMed:19410545}. This is the function of HJURP (Holliday junction recognition protein, Ensembl gene identifier ENSG00000123485).