Nuclear proteins included components

The human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia (ATE) and HTLV-l-associated myelopathy/tropical spastic paraparesis (HAM/ TSP) [69]. HTLV-1 encodes a transactivator. Tax, that is critical for virus replication and plays a central role in the development of ATL and HAM/TSP [69]. Tax does not bind to DNA directly but functions by interacting with a variety of cellular proteins [69]. Many protein-protein interactions of Tax have been determined by mutational analysis including CREB [70-72] and NF-kB [70,72]. To identify all the cellular proteins that interact with Tax, Wu et al. used chromatography, 2D gel electrophoresis, and mass spectrometric analysis of an HTLV-1-infected cell line (C81) [73]. As Tax functions in both the cytoplasm and the nucleus [70,74], Tax-interacting proteins were identified from both cellular compartments. Some of the cytoplasmic proteins included small GTPases and components of the cytoskeleton while some of the more interesting nuclear proteins included components of the SWl/SNF chromatin remodeling complex [73]. 

Membrane proteins (I) (peptides a, b, c in Hoober s nomenclature L-protein, or peptides Va, Vb are synthesized by cytoplasmic 80 S ribosomes (II) and coded for by nuclear DNA (III). The transcription process can be inhibited by actinomycin D, but not by rifampicin. The translation process can occur in the dark and is inhibited by cycloheximide (II). The proteins are transferred to the chloroplast and become incorporated into chloroplast membrane (IV), which as such, are photosynthetically inactive. Activation proteins " synthesized in the chloroplast (V), coded for by chlorplast—as well as nuclear DNA—and translated on 70 S ribosomes inhibited by chloramphenicol are added to the inactive membrane which becomes photosynthetically functional (VI). The activation proteins include components which are essential for the activity of the photosystem II and I reaction centers and can be made and inserted into the growing membrane in absence of concomitant chlorophyll synthesis or protein synthesis in the cytoplasm, provided that the inactive membranes containing the cytoplasmic proteins are already formed. ... 

A small number of proteins, including NCoR and SMRT, comprise the corepressor family. They function, at least in part, as described in Figure 43-2. Another family includes the TRAPs, DRIPs, and ARC (Table 43-6). These so-called mediator-related proteins range in size from 80 kDa to 240 kDa and are thought to be involved in linking the nuclear receptor-coactivator complex to RNA polymerase II and the other components of the basal transcription apparatus. 

Other nonhistone nuclear proteins. Polyacrylamide gel electrophoresis revealed more than 450 components in HeLa cell nuclei. Most are present in small amounts of <10,000 molecules per cell and are not detectable in cytoplasm.112 Among the more acidic proteins are many enzymes including RNA polymerases. There are also gene repressors, hormone-binding proteins, protein kinases, and topoi-somerases.113 Among the six most abundant nonhistone nuclear proteins in the rat are the cytoskeletal proteins myosin, actin, tubulin, and tropomyosin.114... 

EXAMPLE 6.17 A Ub ligase called APC is activated by signaling pathway-dependent phosphorylation as cells approach mitosis. This 3 enzyme catalyzes the attachment of Ub to varions proteins, including lamins that are components of the nuclear membrane. Degradation of lamins allows dissolution of the nuclear membrane, permitting release of chromatids in preparation for mitosis. 

Thus far, microtubules and actin filaments and their associated proteins have been discussed to advantage as independent cytoskeletal components. In actual fact, all of the components of the cytoskeleton (including intermediate filaments) are precisely integrated with one another (Langford, 1995), as well as with various cytoplasmic organelles, the nuclear membrane, the plasma membrane, and the extracellular matrix. In its totality the cytoskeleton subserves many coordinated and regulated functions in the cell ... 

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