The cell nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm; and the nuclear matrix, a network within the nucleus that adds mechanical support.
Chromatin is a complex of DNA and protein found in eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important roles in reinforcing the DNA during cell division, preventing DNA damage, and regulating gene expression and DNA replication. During mitosis and meiosis, chromatin facilitates proper segregation of the chromosomes in anaphase; the characteristic shapes of chromosomes visible during this stage are the result of DNA being coiled into highly condensed chromatin.
Retroviral integrase (IN) is an enzyme produced by a retrovirus that integrates its genetic information into that of the host cell it infects. Retroviral INs are not to be confused with phage integrases (recombinases) used in biotechnology, such as λ phage integrase, as discussed in site-specific recombination.
The nucleoplasm, also known as karyoplasm, is the type of protoplasm that makes up the cell nucleus, the most prominent organelle of the eukaryotic cell. It is enclosed by the nuclear envelope, also known as the nuclear membrane. The nucleoplasm resembles the cytoplasm of a eukaryotic cell in that it is a gel-like substance found within a membrane, although the nucleoplasm only fills out the space in the nucleus and has its own unique functions. The nucleoplasm suspends structures within the nucleus that are not membrane-bound and is responsible for maintaining the shape of the nucleus. The structures suspended in the nucleoplasm include chromosomes, various proteins, nuclear bodies, the nucleolus, nucleoporins, nucleotides, and nuclear speckles.
Lamins, also known as nuclear lamins are fibrous proteins in type V intermediate filaments, providing structural function and transcriptional regulation in the cell nucleus. Nuclear lamins interact with inner nuclear membrane proteins to form the nuclear lamina on the interior of the nuclear envelope. Lamins have elastic and mechanosensitive properties, and can alter gene regulation in a feedback response to mechanical cues. Lamins are present in all animals but are not found in microorganisms, plants or fungi. Lamin proteins are involved in the disassembling and reforming of the nuclear envelope during mitosis, the positioning of nuclear pores, and programmed cell death. Mutations in lamin genes can result in several genetic laminopathies, which may be life-threatening.
Intermediate filaments (IFs) are cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate Branchiostoma.
The nuclear lamina is a dense fibrillar network inside the nucleus of eukaryote 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.
In biology, the nuclear matrix is the network of fibres found throughout the inside of a cell nucleus after a specific method of chemical extraction. According to some it is somewhat analogous to the cell cytoskeleton. In contrast to the cytoskeleton, however, the nuclear matrix has been proposed to be a dynamic structure. Along with the nuclear lamina, it supposedly aids in organizing the genetic information within the cell.
Rous sarcoma virus (RSV) is a retrovirus and is the first oncovirus to have been described. It causes sarcoma in chickens.
Emerin is a protein that in humans is encoded by the EMD gene, also known as the STA gene. Emerin, together with LEMD3, is a LEM domain-containing integral protein of the inner nuclear membrane in vertebrates. Emerin is highly expressed in cardiac and skeletal muscle. In cardiac muscle, emerin localizes to adherens junctions within intercalated discs where it appears to function in mechanotransduction of cellular strain and in beta-catenin signaling. Mutations in emerin cause X-linked recessive Emery–Dreifuss muscular dystrophy, cardiac conduction abnormalities and dilated cardiomyopathy.
Lamina-associated polypeptide 2 (LAP2), isoforms beta/gamma is a protein that in humans is encoded by the TMPO gene. LAP2 is an inner nuclear membrane (INM) protein.
Prelamin-A/C, or lamin A/C is a protein that in humans is encoded by the LMNA gene. Lamin A/C belongs to the lamin family of proteins.
SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 is a protein that in humans is encoded by the SMARCB1 gene.
Barrier-to-autointegration factor is a protein that in humans is encoded by the BANF1 gene. It is a member of the barrier-to-autointegration factor family of proteins.
Scaffold attachment factor B, also known as SAFB, is a gene with homologs that have been studied in humans and mice.
Lamin-B1 is a protein that in humans is encoded by the LMNB1 gene.
The pre-integration complex (PIC) is a nucleoprotein complex of viral genetic material and associated viral and host proteins which is capable of inserting a viral genome into a host genome. The PIC forms after uncoating of a viral particle after entry into the host cell. In the case of the human immunodeficiency virus (HIV), the PIC forms after the Reverse Transcription Complex (RTC) has reverse transcribed the viral RNA into DNA. The PIC consists of viral proteins, host proteins and the viral DNA. The PIC enters the cellular nucleus through the nuclear pore complex without disrupting the nuclear envelope, thus allowing HIV and related retroviruses to replicate in non-dividing cells. Following nuclear entry, the PIC's DNA payload may be integrated into the host DNA as a "provirus".
AIDS is caused by the human immunodeficiency virus (HIV). Individuals with HIV have what is referred to as a "HIV infection". When infected semen, vaginal secretions, or blood come in contact with the mucous membranes or broken skin of an uninfected person, HIV may be transferred to the uninfected person, causing another infection. Additionally, HIV can also be passed from infected pregnant women to their uninfected baby during pregnancy and/or delivery, or via breastfeeding. As a result of HIV infection, a portion of these individuals will progress and go on to develop clinically significant AIDS.
Inner nuclear membrane proteins are membrane proteins that are embedded in or associated with the inner membrane of the nuclear envelope. There are about 60 INM proteins, most of which are poorly characterized with respect to structure and function. Among the few well-characterized INM proteins are lamin B receptor (LBR), lamina-associated polypeptide 1 (LAP1), lamina-associated polypeptide-2 (LAP2), emerin and MAN1.
In molecular biology, the ARID domain ) is a protein domain that binds to DNA. ARID domain-containing proteins are found in fungi, plants and invertebrate and vertebrate metazoans. ARID-encoding genes are involved in a variety of biological processes including embryonic development, cell lineage gene regulation and cell cycle control. Although the specific roles of this domain and of ARID-containing proteins in transcriptional regulation are yet to be elucidated, they include both positive and negative transcriptional regulation and a likely involvement in the modification of chromatin structure. The basic structure of the ARID domain appears to be a series of six alpha-helices separated by beta-strands, loops, or turns, but the structured region may extend to an additional helix at either or both ends of the basic six. Based on primary sequence homology, they can be partitioned into three structural classes: Minimal ARID proteins that consist of a core domain formed by six alpha helices; ARID proteins that supplement the core domain with an N-terminal alpha-helix; and Extended-ARID proteins, which contain the core domain and additional alpha-helices at their N- and C-termini.
