TESTIS BRAIN RNA-BINDING PROTEIN ATTACHES TRANSLATIONALLY REPRESSED AND TRANSPORTED MESSENGER-RNAS TO MICROTUBULES/

We have previously identified a testicular phosphoprotein that binds t o highly conserved sequences (Y and H elements) in the 3' untranslated regions (UTRs) of testicular mRNAs and suppresses in vitro translatio n of mRNA constructs that contain these sequences. This protein, testi s/brain RNA-binding protein (TB-RBP) also is abundant in brain and bin ds to brain mRNAs whose 3' UTRs contain similar sequences. Here we sho w that TB-RBP binds specific mRNAs to microtubules (MTs) in vitro, Whe n TB-RBP is added to MTs reassembled from either crude brain extracts or from purified tubulin, most of the TB-RBP binds to MTs. The associa tion of TB-RBP with MTs requires the assembly of MTs and is diminished by colcemid, cytochalasin D, and high levels of salt; Transcripts fro m the 3' UTRs of three mRNAs that contain the conserved sequence eleme nts (transcripts for protamine 2, tau protein, and myelin basic protei n) are linked by TB-RBP to MTs, whereas transcripts that lack the cons erved sequences do not bind TB-RBP. We conclude that TB-RBP serves as an attachment protein for the MT association of specific mRNAs, Consid ering its ability to arrest translation in vitro, we propose that TB-R BP functions in the storage and transportation of mRNAs to specific in tracellular sites where they are translated.