Dynamic associations of heterochromatin protein 1 with the nuclear envelope

To study the dynamics of mammalian HP1 proteins we have microinjected recom binant forms of mHP1 alpha, M31 and M32 into the cytoplasm of living cells. As could be expected from previous studies, the three fusion proteins were efficiently transported into the nucleus and targeted specific chromatin a reas. However, before incorporation into these areas the exogenous proteins accumulated in a peripheral zone and associated closely,vith the nuclear e nvelope. This transient association did not occur when the cells were treat ed with deacetylase inhibitors, indicating an acetylation-inhibited interac tion. In line with these observations, recombinant HP1 proteins exhibited s aturable binding to purified nuclear envelopes and stained the nuclei of de tergent-permeabilized cells in a rim-like fashion. Competition experiments with various M31 mutants allowed mapping of the nuclear envelope-binding si te within an N-terminal region that includes the chromodomain. A His(6)-tag ged peptide representing this region inhibited recruitment of LAP2 beta and B-type lamins around the surfaces of condensed chromosomes, suggesting inv olvement of HP1 proteins in nuclear envelope reassembly.