Trax (Translin-associated Factor X), a Primarily Cytoplasmic Protein, Inhibits the Binding of TB-RBP (Translin) to RNA

Abstract

Trax (Translin-associated factor X) has been shown to interact with TB-RBP/Translin by its coimmunoprecipitation and in yeast two-hybrid assays. Here we demonstrate that Trax is widely expressed, does not bind to DNA or RNA, but forms heterodimers with TB-RBP under reducing conditions. The heterodimer of TB-RBP and Trax inhibits TB-RBP binding to RNA, but enhances TB-RBP binding to specific single stranded DNA sequences. The in vitro interactions between TB-RBP and Trax are confirmed by similar interactions in the yeast two-hybrid system. Cell fractionation and confocal microscope studies reveal that Trax is predominantly cytoplasmic. In contrast, TB-RBP is present in both the nuclei and cytoplasm of transfected cells and uses a highly conserved nuclear export signal to exit nuclei. In addition to a leucine zipper, two basic domains in TB-RBP are essential for RNA binding, but only one of these domains is needed for DNA binding. Trax restores DNA binding to TB-RBP containing an altered form of this domain. These data suggest that Trax-TB⅐RBP interactions modulate the DNA-and RNA-binding activity of TB-RBP.The process of mammalian spermatogenesis is highly organized spatially and temporally. Highly controlled transcription and protein expression occur in each developmental stage. During the haploid interval, spermiogenesis, the spermatids become transcriptionally inactive, although there is a need for the synthesis of many proteins essential for the formation of spermatozoa (1). The sex chromosomes encode numerous genes essential for gametogenesis. Because the spermatids are haploid cells, they contain either the X or Y chromosome. Thus, intercellular transport of mRNA in the haploid cells is a critical process to ensure genetic equivalency.The testis brain RNA-binding protein (TB-RBP) 1 was identified and cloned on the basis of its ability to bind H and Y sequence elements in the 3Ј-untranslated repeats of mouse protamine 1 and 2 mRNAs (2). TB-RBP is the mouse orthologue of human Translin, a single-stranded DNA-binding protein that binds consensus sequence breakpoint junctions of chromosomal translocations in lymphoid malignancies (3). The TB-RBP/Translin consensus binding sequences are also found in TLS-CHOP reciprocal translocations, in therapy-related translocations in acute myeloid leukemias, and in BCR-ABL translocations in chronic myeloid leukemia (4 -6). Sequence analysis in a meiotic recombination hot spot region of human chromosome 16 shows TB-RBP/Translin binding sequences near the breakpoint (7). TB-RBP/Translin has also been proposed to act as a single-stranded DNA-binding transcription factor, which activates early response gene expression in the brain (8). TB-RBP/Translin also functions as a RNA-binding protein mediating intracellular and intercellular mRNA transport (9, 10). RNA binding of TB-RBP has been observed in brain and testis, and the binding is dependent upon Y and H sequence elements (2). Many testis-and brain-specific mRNAs have Y and H consensus sequences, and specific RNA⅐TB-RBP inter...

The DISC locus in psychiatric illness

“…57,61 The TSNAX gene produces a 33 kDa protein that binds and modulates the DNA/ RNA binding activity of the nucleic acid binding protein Translin. 62,63 Translin/Trax complexes are highly expressed in brain, where they are implicated in dendritic mRNA translation. 64 These trans splicing events are rare and although they produce novel fusion transcripts, they are low in abundance and translation products have yet to be documented.…”

Translin-associated Factor X Is Post-transcriptionally Regulated by Its Partner Protein TB-RBP, and Both Are Essential for Normal Cell Proliferation

“…DISCUSSION TB-RBP/Translin is ubiquitously expressed in the mouse and has been proposed to function as both a DNA-and RNA-binding protein suggesting multiple functions. Its associated partner TRAX, first characterized as a Translin-like protein (16), forms DNA-and RNA-binding complexes with Translin (17,18) and has been proposed to function in DNA repair in conjunction with the nuclear matrix protein C1D (19).…”

“…Plasmid Constructs-Wild type TB-RBP was subcloned into pEGFP-C2 (Clontech, Palo Alto, CA) (17). Mouse TRAX cDNA was ob-tained by RT-PCR from mouse testis RNA using a pair of primers containing EcoRI and BamHI sites and subcloned into pDsRed2-N1 and pEGFP-N1 (Clontech, Palo Alto, CA).…”

“…The level of Translin has been demonstrated to closely parallel the proliferative state of somatic cells with its induced overexpression in HEK 293 cells accelerating cell proliferation (15). TRAX, first characterized as a Translin-like protein (16), forms DNA and RNA binding complexes with Translin (17,18). TRAX has been proposed to function in DNA repair in conjunction with the nuclear matrix protein C1D (19).…”

Functional Characterization of Drosophila Translin and Trax

“…Accordingly, it is thought to play a role in the subcellular transport and/or translational control of its target RNAs in these tissues (Han et al 1995a;Kobayashi et al 1998;Morales et al 1998;Muramatsu et al 1998;Wu and Hecht 2000;Yang et al 2003). Unlike Translin, Trax does not bind nucleic acids directly, but might be part of the RNA-or DNA-binding complex, thereby modulating the nucleic-acid-binding affinity of Translin (Chennathukuzhi et al 2001;Finkenstadt et al 2002;Gupta et al 2005).…”