Nucleohyaloplasm
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Nucleohyaloplasm is the cytosol within the nucleus, without the microfilaments and the microtubules. This liquid part contains enzymes and intermediate metabolites. Many substances such as nucleotides (necessary for purposes such as the replication of DNA and production of mRNA) and enzymes (which direct activities that take place in the nucleus) are dissolved in the nucleohyaloplasm.
As a cytosol, it consists mostly of water, dissolved ions, small molecules, and large water-soluble molecules (such as protein). It contains about 20% to 30% protein. It has a high concentration of K⁺ ions and a low concentration of Na⁺ ions.
Small particles
Small particles (< 30 kDa) are able to pass through the nuclear pore complex by passive transport.
In addition to sodium and potassium ions the nucleohyaloplasm contains Mg2+[1]. Some of these ions are associated with incoming ribonucleoside triphosphate (NTP) as they enter the catalytic center for transcription by RNA polymerase (RNAP) II.[1]
The average mass range for amino acids: 75 - 204 Da. By comparison a water molecule is 18 Da. Nucleotides range in size from 176 Da (OMP) to 523 Da (GTP). The lateral speed of biological molecules in passive diffusion in water is on the order of 500 - 50 nm/sec. But in cytosol such as the nucleohyaloplasm: ~120 - 10 nm/sec due to crowding and collisions with large molecules.
Large particles
Larger particles are also able to pass through the large diameter of a nuclear pore but at almost negligible rates.[2]
The lamins of mammalian nuclei are polypeptides of 60-80 kDa: A (70 kDa), B (68 kDa), and C (60 kDa).[3] A- and B-type lamins, which form separate, but interacting, stable meshworks in the lamina, have different mobilities.[4]
Euchromatin is the less compact DNA form, and contains genes that are frequently expressed by the cell.[5] Active genes, which are generally found in the euchromatic region of the chromosome, tend to be located towards the chromosome's territory boundary.[6]
Heterochromatin is usually localized to the periphery of the nucleus along the nuclear envelope. It mainly consists of genetically inactive satellite sequences,[7] and many genes are repressed to various extents, although some cannot be expressed in euchromatin at all.[8]
Structures
Of the structures local to the nucleohyaloplasm, some serve to confine it such as the inner membrane of the nuclear envelope. While others are completely suspended within it, for example, the nucleolus. Still others such as the nuclear matrix[9][10] and nuclear lamina are found throughout the inside of the nucleus.
Lamins within the nucleohyaloplasm form another regular structure the nucleoplasmic veil[11]. The veil is excluded from the nucleolus and is present during interphase.[12] The lamin structures that make up the veil bind chromatin and disrupting their structure inhibits transcription of protein-coding genes.[13] Changes also occur in the lamina mesh size.[4]
Besides the nucleolus, the nucleus contains a number of other non-membrane delineated bodies. These include Cajal bodies, Gemini of coiled bodies, polymorphic interphase karyosomal association (PIKA), promyelocytic leukaemia (PML) bodies, paraspeckles and splicing speckles. Although little is known about a number of these domains, they are significant in that they show that the nucleohyaloplasm is not a uniform mixture, but rather contains organized functional subdomains.[14]
References
- ↑ 1.0 1.1 Langelier MF, Baali D, Trinh V, Greenblatt J, Archambault J, Coulombe B (2005). "The highly conserved glutamic acid 791 of Rpb2 is involved in the binding of NTP and Mg(B) in the active center of human RNA polymerase II". Nucleic Acids Res. 33 (8): 2629–39. PMID 15886393. Unknown parameter
|month=ignored (help) - ↑ Campbell, Neil A. (1987). Biology. p. 795. ISBN 0-8053-1840-2.
- ↑ Klaus Urich (1994). Comparative Animal Biochemistry. Springer. p. 359. ISBN 3540574204, 9783540574200 Check
|isbn=value: invalid character (help). - ↑ 4.0 4.1 Shimi T, Pfleghaar K, Kojima S, Pack CG, Solovei I, Goldman AE, Adam SA, Shumaker DK, Kinjo M, Cremer T, Goldman RD (2008). "The A- and B-type nuclear lamin networks: microdomains involved in chromatin organization and transcription". Genes Dev. 22 (24): 3409–21. PMID 19141474. Unknown parameter
|month=ignored (help) - ↑ Ehrenhofer-Murray A (2004). "Chromatin dynamics at DNA replication, transcription and repair". Eur J Biochem. 271 (12): 2335–2349. doi:10.1111/j.1432-1033.2004.04162.x. PMID 15182349.
- ↑ Kurz A , Lampel S, Nickolenko JE, Bradl J, Benner A, Zirbel RM, Cremer T, Lichter P (1996). "Active and inactive genes localize preferentially in the periphery of chromosome territories". J of Cell Biol. The Rockefeller University Press. 135: 1195–1205. doi:10.1083/jcb.135.5.1195. PMID 8947544.
- ↑ Lohe, A.R.; et al. (1993). "Mapping simple repeated DNA sequences in heterochromatin of Drosophila melanogaster". Genetics. 134 (4): 1149–1174. ISSN 0016-6731. PMID 8375654.
- ↑ Lu, B.Y.; et al. (2000). "Heterochromatin protein 1 is required for the normal expression of two heterochromatin genes in Drosophila". Genetics. 155 (2): 699–708. ISSN 0016-6731. PMID 10835392.
- ↑ Nickerson J (2001). "Experimental observations of a nuclear matrix". J. Cell. Sci. 114 (Pt 3): 463–74. PMID 11171316. Unknown parameter
|month=ignored (help) - ↑ Tetko IV, Haberer G, Rudd S, Meyers B, Mewes HW, Mayer KF (2006). "Spatiotemporal expression control correlates with intragenic scaffold matrix attachment regions (S/MARs) in Arabidopsis thaliana". PLoS Comput. Biol. 2 (3): e21. doi:10.1371/journal.pcbi.0020021. PMC 1420657. PMID 16604187. Unknown parameter
|month=ignored (help) - ↑ Goldman R, Gruenbaum Y, Moir R, Shumaker D, Spann T (2002). "Nuclear lamins: building blocks of nuclear architecture". Genes Dev. 16 (5): 533–547. doi:10.1101/gad.960502. PMID 11877373.
- ↑ Moir RD, Yoona M, Khuona S, Goldman RD. (2000). "Nuclear Lamins A and B1: Different Pathways of Assembly during Nuclear Envelope Formation in Living Cells". Journal of Cell Biology. 151 (6): 1155–1168. doi:10.1083/jcb.151.6.1155. PMID 11121432.
- ↑ Spann TP, Goldman AE, Wang C, Huang S, Goldman RD (2002). "Alteration of nuclear lamin organization inhibits RNA polymerase II–dependent transcription". J of Cell Biol. 156 (4): 603–608. doi:10.1083/jcb.200112047. PMID 11854306.
- ↑ Dundr M, Misteli T (2001). "Functional architecture in the cell nucleus". Biochem J. (356): 297–310. doi:10.1146/annurev.cellbio.20.010403.103738. PMID 11368755.