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The nuclear lamina is a dense (~30 to 100 nm thick) fibrillar network inside the nucleus of most cells. It is composed of intermediate filaments and membrane associated proteins. Besides providing mechanical support, the nuclear lamina regulates important cellular events such as DNA replication and cell division. Additionally, it participates in chromatin organization and it anchors the nuclear pore complexes embedded in the nuclear envelope. Plants or single-cell Eukaryotic organisms such as ''Saccharomyces cerevisiae'' lack lamins. The nuclear lamina is separated with the inner face of the bilayer nuclear envelope whereas the outer face stays continuous with the endoplasmic reticulum.〔The Cell: A Molecular Approach, Cooper & Hausman. 5th Edition. Pg. 357〕 == Structure and composition == The nuclear lamina consists of two components, lamins and nuclear lamin-associated membrane proteins. The lamins are type V intermediate filaments which can be categorized as either A-type (lamin A, C) or B-type(lamin B1, B2) according to homology in sequence, biochemical properties and cellular localization during the cell cycle. Type V intermediate filaments differ from cytoplasmic intermediate filaments in the way that they have an extended rod domain (42 amino acid longer), that they all carry a nuclear localization signal (NLS) at their C-terminus and that they display typical tertiary structures. Lamin polypeptides have an almost complete α-helical conformation with multiple α-helical domains separated by non-α-helical linkers that are highly conserved in length and amino acid sequence. Both the C-terminus and the N- terminus are non α-helical, with the C-terminus displaying a globular structure. Their molecular weight ranges from 60 to 80 kilodaltons (kDa). In the amino acid sequence of nuclear lamins, there are also two phosphoacceptor sites present, flanking the central rod domain. A phosphorylation event at the onset of mitosis leads to a conformational change which causes the disassembly of the nuclear lamina. (discussed later in the article) In the vertebrate genome, lamins are encoded by three genes. By alternative splicing, at least seven different polypeptides (splice variants) are obtained, some of which are specific for germ cells and play an important role in the chromatin reorganisation during meiosis. Not all organisms have the same number of lamin encoding genes; ''Drosophila melanogaster'' for example has only 2 genes, whereas ''Caenorhabditis elegans'' has only one. The presence of lamin polypeptides is an exclusive property of Metazoan organisms. The nuclear lamin-associated membrane proteins are either integral or peripheral membrane proteins. The most important are lamin associated polypeptide 1 and 2 (LAP1, LAP2), emerin, lamin B-receptor (LBR), otefin and MAN1. Due to their positioning within or their association with the inner membrane, they mediate the attachment of the nuclear lamina to the nuclear envelope. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「nuclear lamina」の詳細全文を読む スポンサード リンク
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