HnRNP Al protein

A EXPERIMENTAL FIGURE 12-22 The movement of human hnRNP Al protein between nuclei in a heterokaryon shows that it can cycle in and out of the cytoplasm, but human hnRNP C protein, which showed no such movement, cannot. Cultured HeLa cells and Xenopus cells were fused by treatment with polyethylene glycol, producing heterokaryons containing nuclei from each cell type. The hybrid cells were treated with cycloheximide Immediately after fusion to prevent protein synthesis. After 2 hours, the cells were fixed and stained with fluorescent-labeled antibodies specific for human hnRNP C and Al proteins. These antibodies do not bind to the homologous Xenopus proteins, (a) A fixed preparation viewed by phase-contrast microscopy Includes unfused HeLa cells (arrowhead) and Xenopus cells (dotted arrow), as well as fused heterokaryons... 

Stutz, F., Bachi, A., Doerks, T., Braun, I.C., Seraphin, B., Wilm, M. et al. (2000) REF, an evolutionary conserved family of hnRNP-like proteins, interacts with TAP/Mex67p and participates in mRNA nuclear export. RNA, 6, 638-650. 

Fig. 1 Representative splicing cu-elements and tran -factors. Tissue-specific and developmental stage-specific expressions of splicing trans-factors including SR proteins and hnRNP Al enable precise regulations of alternative splicing. ISE and ISS have similar activities as ESE and ESS, but are omitted firom the figure...

MK2 (also termed MAP kinase-activated protein kinase 2, MAPKAP-K2) is activated by p38 MAP kinase a// (Kotlyarov et al, 2002 Roux and Blenis, 2004). MK2 plays a key role in the control of the production of certain cytokines, for example, tumor necrosis factor a. MK2 does so by phosphorylating proteins that bind specifically to the regulatory regions in the S untranslated regions (UTRs) of such mRNAs (Hitti et al, 2006). These regions contain AU-rich elements (AREs) to which proteins such as HnRNP A1 also bind. 

In a patient with congenital myasthenic syndrome, we identified that CHRNAl IVS3-8G>A attenuates binding of hnRNP /f 100-fold and causes exclusive inclusion of the downstream exon P3A (Masuda et al., 2008) (Fig. 4). We also identified that polypyrimidine tract binding protein (PTB) silences recognition of exon P3A and tannic acid facilitates the expression of PTB by activating its promoter region (Gao et al., 2009). 

Two dimensional (2D) Northwestern blotting complements gel-shift experiments in the identification of specific protein-nucleic acid interactions. The procedures described below, which have been adapted from the protocol described by Schenkel et al. (1988), have been valuable in our laboratory for the identification of several hnRNP proteins (our unpublished observations). Here, we demonstrate the technique on 2D gel blots of transformed human amnion (AMA) cell proteins (Fig. 1) using poly(rC), a homopolymer that interacts with hnRNPs K and L (Matunis et al., 1992 Dejgaard et al., 1994), as well as poly(rU), which interact with hnRNPs C and M (Swanson and Dreyfuss, 1988 Dreyfuss et al., 1993). The technique works equally well, however, when sequence-specific deoxyoligonucleotides are used as probes. 

If none of the normal processing reactions that modify a pre-mRNA chain are inhibited by adenovirus infection, then it would seem that the virus must induce either selective transport of viral mRNA or a mechanism that discriminates among viral and cellular species at some prior step, upon which transport itself depends. Examples of the latter class of mechanism might include incomplete or incorrect packaging of cellular transcripts with nuclear proteins for form hnRNP or the displacement of cellular RNA molecules from their normal site(s) of synthesis or processing within the nucleus (for example, attached to a structure such as the nuclear matrix Herman et al., 1978 Miller et al., 1978 van Eekelen and van Venrooij, 1981 Jackson et al., 1981, 1982 Maniman et al., 1982.). Experimental evidence that addresses either of these possibilities directly is not available. It does, however, seem clear that hnRNP populations isolated from adenovirus-infected cells do not comprise solely viral RNA se-... 

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