Protein-protein interactions between the testis brain RNA-binding protein and the transitional endoplasmic reticulum ATPase, a cytoskeletal gamma actin and Trax in male germ cells and the brain

Numerous functions have been proposed for the testis brain RNA-binding prot ein (TB-RBP) and its human homologue, Translin, ranging from mRNA transport and translational regulation to DNA rearrangement and repair. To gain insi ght into the likely functions of this 26 kDa protein, immunoprecipitation w as used to identify proteins that interact with TB-RBP in mouse cytosolic e xtracts. Three proteins, the transitional endoplasmic reticulum ATPase, a c ytoskeletal gamma actin, and Trax, were specifically immunoprecipitated wit h an affinity-purified antibody to recombinant mouse TB-RBP. In vitro bindi ng assays with recombinant proteins and EM immunocytochemistry confirm that TB-RBP interacts with the TER ATPase in vitro and in vivo. Confocal micros copy has demonstrated that TB-RBP colocalizes with actin in the cytoplasm o f male germ cells, The immunoprecipitation of Trax with TB-RBP confirms a p ublished report demonstrating protein interactions between the two proteins in a yeast two-hybrid assay. These data support the hypothesis that TB-RBP serves as a link in attaching specific mRNAs to cytoskeletal structures an d suggests an involvement for the ubiquitously expressed TER ATPase in intr acellular and/or intercellular mRNA transport.