Protein import, nucleus roles

The viral protein Rev may also play a role in HIV-1 latency. Expression of the viral Rev protein is essential for the nuclear export of genomic RNA as well as unspliced and/or singly spliced transcripts (Cullen 2003), which are ultimately translated into structural, regulatory, and enzymatic viral proteins. Retention of Rev and Tat (viral transactivator proteins) transcripts in the nucleus of resting CD4h- T cells from HAART patients (Lassen et al. 2006) might be involved in the maintenance of post-integration latency in these cells. Importantly, this phenomenon is non-existent in activated T cells. 

As was mentioned earlier, DAG activates protein kinase C, which phosphorylates transcription factors like NFjcB nuclear transcription factor. NFjcB forms a multisubunit complex with an inhibitory subunit which is phosphorylated by PKC. The complex disintegrates and what is released translocates to the nucleus and initiates gene transcription. NFjcB is a heterodimer, with two distinct DNA-binding subunits 50 kDa and 65 kDa, both being members of the Rel transcription factor family. These proteins have an important role in the signaling cascade of the cellular defense system, and activate numerous genes in response to pathogens or inflammatory cytokines. 

Lipid modified proteins are often attached to cell membranes. In many cases, they play crucial roles in the transduction of extracellular signals across the plasma membrane and into the nucleus. A particularly important example are the N-, K-, and H-Ras proteins. All Ras proteins terminate in a fame... 

More recent studies in Drosophila revealed that H3.3 also plays an important role in the male pronucleus after fertilization (Loppin et al. 2005). The loss of the H3.3 chaperone HIRA impairs the replacement of paternal non-histone proteins from the sperm nucleus with maternally provided histones including H3.3, while the maternal genome exclusively contains the canonical H3. Thus, H3.3 and its deposition factor HIRA function in early fertilization events and might have a role in imprinting in higher eukaryotes. 

Cysteine disulfide formation is one of the most important posttranslational modifications involved in protein structure. Disulfides play a crucial role in maintaining the structure of many proteins including insulin, keratin, and many other structurally important proteins. While the cytoplasm and nucleus are reducing microenvironments, the Golgi and other organelles can have oxidizing environments and process proteins to contain disulfide bonds (Scheme 5). 

The spectrum of pleiotropic functions of different HI variants in different taxa has yet to be established. With respect to interactions within chromatin, the elucidation of the role of linker histones in transmitting or enhancing the effects of other non-histone proteins will be of particular interest. Given the dynamic behavior of HI in the nucleus, the possibility of auxiliary extrachromosomal functions performed by the free HI pool should be explored. An example of such a function is the recent finding that free HI is involved in the import of adenovirus DNA into the nucleus [158]. Other potential functions, especially at the period of maximum chromatin condensation, could depend on the gradient of free HI around the chromosomes. 

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