Abstract
Replicated mammalian chromosomes condense to segregate during anaphase, and they de-condense at the conclusion of mitosis. Currently, it is not understood what the factors and events are that specify de-condensation. Here, we demonstrate that chromosome de-condensation needs the function of an inner nuclear membrane (INM) protein hsSUN1 and a membrane associated histone acetyltransferase (HAT), hALP. We propose that nascently reforming nuclear envelope employs hsSUN1 and hALP to acetylate histones for de-compacting DNA at the end of mitosis. The eukaryotic nucleus is separated from other organelles by an envelope containing two membrane layers continuous with the endoplasmic reticulum. Nuclear membrane proteins fall into three categories according to their localization. The first group is the trans-nuclear membrane proteins resident in the nuclear pore complex (NPC). 2 The second group contains the inner membrane proteins (INM), which include the lamin B receptor (LBR), emerin, and lamin-associated polypeptides (LAPs). The third group includes proteins underlying the nuclear membrane such as nuclear lamina (1). Functionally, the INM provides a physical barrier; the NPC serves for the transport of material between the nucleus and the cytoplasm (2); and the nuclear lamina erects a meshwork, which maintains nuclear structure and assists indirectly in DNA replication and RNA processing (3, 4). Most INM proteins are associated with the nuclear lam-ina. In a proteomic study of INM proteins, in addition to 13 known proteins, 67 uncharacterized open reading frames (ORFs) were identified (5)