👤 Dominika O Trembecka-Lucas

Heterochromatin protein 1 (HP1), a small non-histone chromosomal protein, was recently shown to form a complex in vivo with Proliferating Cell Nuclear Antigen (PCNA), a key factor in DNA replication. The complex, which requires HP1β in a form of a dimer, is engaged in DNA repair and replication. We now provide further evidence based on FRET-FLIM live cell studies confirming the association and close proximity between HP1β and PCNA in the complex. We also demonstrate using FRAP, that although HP1β-PCNA complexes are highly mobile in nonreplicating nuclei, when engaged in DNA replication, they become bound and do not exchange with the mobile pool. These observations are in agreement with a notion that a subpopulation of HP1 molecules interact with PCNA in vivo during DNA replication. Similarly, HP1β which is associated with PCNA in regions of DNA repair, is bound and does not exchange with the mobile pool, suggesting that HP1β in association with PCNA may be a component of a DNA repair complex. Show less

Heterochromatin protein 1 (HP1) is a small non-histone chromosomal protein known as a dominant suppressor of position-effect variegation and a major component of heterochromatin. Posttranslationally modified HP1, through interaction with protein partners from different groups, can be involved in a number of nuclear processes, including gene activation, chromatin remodeling, replication and DNA repair. Using bimolecular fluorescence complementation assay and live cell imaging, we demonstrate that HP1β and PCNA, a key player in DNA replication, are closely spaced components of a multiprotein complex involved in replication, both in S phase and during DNA repair, and that the functional complex requires formation of an HP1 dimer. Show less