Cytoplasmic repression

X. laevis rRNA is able to repress X. mulleri rRNA activity as well as the maternal cytoplasm. This was demonstrated in experiments using X. laevis normal females and females with a deletion of the nucleolar organizer (1 -strain). When X. laevis rDNA is present, this inhibition is permanent. Cytoplasmic repression, on the other hand, is reversible and, as a rule, only temporary (Honjo and Reeder,... 

Mazroui, R., Huot, M. E., Tremblay, S., Filion, C., Labelle, Y., and Khandjian, E. W. (2002). Trapping of messenger RNA by Fragile X Mental Retardation protein into cytoplasmic granules induces translation repression. Hum. Mol. Genet. 11, 3007—3017. 

Figure 3. The many ways to lose a HAT. Decreased amounts of functional CBP protein and subsequent CBP s loss of function has been observed in different contexts of neurological disorders and neuronal apoptosis. RTS (Rubinstein-Taybi Syndrome) results from a mutation on one cbp gene allele. In several cases of polyQ diseases, CBP can be sequestred by the mutated polyQ proteins, forming aggregates in the cytoplasm or the nucleus. CBP proteasomal degradation was also shown to be favored by polyQ proteins. CBP is a caspase-6 substrate in cerebellar granule neurons (CGN) deprived of potassium modeling caspase-dependent apoptosis. Finally, cbp gene repression has been observed in oxidative stress-induced death of a motomeuronal cell line. The mechanisms by which CBP levels are reduced in motomeurons of ALS mice is still unknown...

The Protein Coat. Twenty-four polypeptides assemble into a hollow sphere, of ca. 100-120 X in outer diameter, to form the protein coat of ferritin. The diameter of the interior, which becomes filled with hydrous ferric oxide, is ca. 70-80 A. Subunit assembly appears to be spontaneous the coat remains assembled even without the iron core. Subunit biosynthesis is actually controlled by the amount of iron to be stored by a cell the subunit templates (mRNAs) are stored in the cytoplasm of a cell in a repressed form and are recruited for biosynthesis when the concentration of iron increases (3). 

E. coli uses nitrate as a terminal electron acceptor through a respiratory, dissimilatory nitrate reductase whose synthesis is induced when nitrate is provided, and which is repressed by oxygen. Nitrate reductase is discussed with other molybdoenzymes in Section 62.1.9, and catalyzes the reduction of nitrate to nitrite. The enzyme is isolated from the cytoplasmic membrane of E. coli, and contains three subunits (a, j8 and y) although the y-subunit may be absent in some preparations. The -y-subunit is a b-type cytochrome, and the a-subunit is reported to be the catalytic subunit. The enzyme contains a number of iron-sulfur clusters, including a HiPIP and at least two ferredoxins.1054,1437... 

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