Nuclear binding

NF-xB, originally defined as the enhancer of kappa light-chain expression in B lymphocytes, is a hcterodimeric protein that can rapidly activate several genes associated with the inflammatory process (reviewed by Schreck et al., 1992). The DNA binding, nuclear form, of NF-xB is a heterodimer composed of one Rel-A (65 kD) and one p50 (50 kD) subunit. However, both subunits can form homodimers that also have DNA-binding activity. The inactive form of NF-xB in non-stimulated cells is localized to the cytoplasm of resting cells, and is bound to its inhibitor IxB. 

The steroid hormone receptors are phophoproteins which are usually phosphorylated on several positions. The phosphorylation sites are mainly foimd in the N-terminal region of the receptors. Serine phosphorylation prevails. One rare example of tyrosine phosphorylation is described for the case of estrogen receptors. The consequences of phosphorylation for the receptor proteins are varied. It is conceivable, and in some cases experimentally proven, that it has influence on hormone binding, nuclear transport, DNA binding and transactivation. 

Moroianu, J., Hijikata, M., Blobel, G. and Radu, A. (1995) Mammalian karyopheiin alb and a2b heterodimers al or a2 subunit binds nuclear localization signal and b subunit interacts with peptide repeat-containing nucleoporins. I roc. Natl. Acad. Sci. USA, 92, 6532-6536. 

Ginsenosides belong to a family of steroids and share their structural characteristics. They can traverse cell membranes freely similar to steroids. Moreover, their presence has been demonstrated within cells, particularly the nucleus. Steroid hormone action, steroids that bind nuclear receptors, are thought to affect primarily the transcription of mRNA and subsequent protein synthesis. Intracellular steroid-binding proteins present possible attractive targets for ginsenosides. 

Hyperforin has been shown to increase the activity of CYP3 A4 and CYP2C9 by binding nuclear receptors that regulate gene expression of certain CYP-encoding genes.18 As a result, St. John s Wort can have the opposite effect as cimetidine. Patients who take St. John s Wort in conjunction with their prescribed medicines may find that their... 

Apart from direct activation via ligand binding, nuclear receptors are also subject to regulation by phosphorylation. Thus, transcriptional activity of PPARy can be regulated by growth factor stimulation via the mitogen-activated protein (MAP) kinase pathway (34). 

The most extensively studied hormone reponsive elements are found = 200 bp from the transcription start site in the long terminal repeat (LTR) of the mouse mammary tumor virus (MMTV). They are responsive to GR as shown by in vitro DNA binding studies with purified GR [131-133] and by in vivo response data with deletion mutants [134—139], From these studies three important functional domains in the LTR of MMTV have been identified two binding sites for GR - a promoter distal binding site and a promoter proximal binding site - and a third site which binds nuclear factor-one (NF-1). 

LOPES CARDOSO, M.I., MEUER, A.H., RUEB, S., MACHADO, J.A., MEMELINK, J., HOGE, J.H.C., A promoter region that controls basal and elicitor-inducible expression levels of the NADPH cytochrome P450 reductase gene (Cpr) from Catharanthus roseus binds nuclear factor GT-1. Mol. Gen. Genet., 1997, 256, 674-681. 

PASQUALI, G ERVEN, A.S., OUWERKERK, P.B., MENKE, F.L., MEMELINK, J., The promoter of the strictosidine synthase gene from periwinkle confers elicitor-inducible expression in transgenic tobacco and binds nuclear factors GT-1 and GBF. Plant Mol. Biol., 1999,39, 1299-1310. 

From an electrostatic point of view, it is amazing that positively charged protons can be packed so closely together. Yet many nuclei do not spontaneously decompose, so they must be stable. In the early twentieth century when Rutherford postulated the nuclear model of the atom, scientists were puzzled by such a situation. Physicists have since detected many very short-lived subatomic particles (in addition to protons, neutrons, and electrons) as products of nuclear reactions. Well over 100 have been identified. A discussion of these many particles is beyond the scope of a chemistry text. Furthermore their functions are not entirely understood, but it is now thought that they help to overcome the proton-proton repulsions and to bind nuclear particles (nucleons) together. The attractive forces among nucleons appear to be important over only extremely small distances, about 10 cm. 

On the level of quantum mechanics we are faced with the problem of solving numerically the Dirac equation governing the time-evolution of an electron state V (f)) under the influence of a space-time-dependent (classical) electromagnetic field AgXt(r, t) including the binding nuclear potential AnUC(r) ... 

Adam, S. A., and Gerace, L. (1991). Cytosolic proteins that specifically bind nuclear localization sequences are receptors for nuclear import. Cell (Cambridge, Mass.) 66, 837-847. 

These observations indicate that fission of metal clusters occurs when the repulsive Coulomb forces due to the accumulation of the excess charges overcome the electronic binding (cohesion) of the cluster. This reminds us immediately of the well-studied nuclear fission phenomenon and the celebrated liquid drop model (LDM) according to which the binding nuclear forces are expressed as a sum of volume and surface terms, and the balance between the Coulomb repulsion and the increase in surface area upon volume-conserving deformations allows for an estimate of the stability and fissility of the nucleus [12, 13]. 

Levy, M. et al. (2005) Arabidopsis IQDl, a novel calmodulin-binding nuclear protein, stimulates glucosinolate accumulation and plant defense. Plant J. 43, 79-96... 

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