Mitotic Regulator Mis18β Interacts with and Specifies the Centromeric Assembly of Molecular Chaperone Holliday Junction Recognition Protein (HJURP)

Abstract

Background: HJURP is a molecular chaperone essential for the deposition of the centromere marker CENP-A. Results: Mis18␤ binds with and specifies the centromere localization of HJURP. Conclusion: Mis18␤ governs centromere assembly via the Mis18␤-HJURP-CENP-A axis. Significance: Our finding reveals a novel mechanism underlying CENP-A incorporation into the centromere.

CRL4RBBP7 is required for efficient CENP-A deposition at centromeres

“…HJURP is known to function in prenucleosomal CENP-A stabilization and in centromere deposition, by a mechanism that requires its dimerization (Zasadzińska et al, 2013), its binding to Mis18b (also known as OIP5) (Wang et al, 2014) and its DNA-binding activities (Müller et al, 2014). HJURP specifically recognizes CENP-A by interacting with the centromere-targeting domain (CATD; Black et al, 2007) of CENP-A to protect it from proteolysis (Foltz et al, 2009).…”

Identification of the Post-translational Modifications Present in Centromeric Chromatin

“…Existing CENP-A nucleosomes directly recruit CENP-C, which in turn recruits the Mis18 complex during mitotic exit (6,7). Mis18 binding recruits HJURP and directs nascent CENP-A nucleosome assembly at an adjacent site (8). Despite the essential presence of the CENP-A nucleosome for centromere formation and maintenance, the centromere-specific nucleosomes are present within a context of chromatin containing post-translational modifications (PTMs) of histones that are thought to be important for centromere function, as outlined below.…”

The role of the Mis18α-β complex and its interactions with HJURP and CENP-A in human centromeric chromatin establishment

“…In fission yeast it was revealed that Scm3 could directly binding to Mis18 in vitro 78 . Our lab, along with others 60 , have established that the Mis18 complex does indeed have a direct interaction with HJURP in vitro and in vivo. These findings will be explained more in the second chapter of this work.…”

“…In this system Scm3 also binds to AT-rich DNA (which is enriched at budding yeast point centromeres) which could make this another avenue for Scm3 recruitment to centromeres 82 . Our lab (in specific the research in this paper) has found Mis18 and Scm3 interact in fission yeast and this interaction is conserved to humans where HJURP directly binds to the Mis18α-β complex 60 . We will show in this thesis that the physical interaction between Mis18 and HJURP/Scm3 is absolutely required for proper HJURP centromere recruitment and CENP-A deposition.…”

“…Inhibition of Cdk activity in both human and chicken cells cause premature loading of the CENP-A deposition machinery and CENP-A during G2-phase 59 . Giving even more credibility to this, it was found that HJURP is phosphorylated by Cdk1 which weakens its interaction with Mis18β, and the interaction of HJURP with the Mis18 complex is key for its recruitment to centromeres 60 . Other factors outside of Cdk's have also been shown to be important for CENP-A deposition in G1-phase.…”