Mouse testis brain ribonucleic acid-binding protein/translin colocalizes with microtubules and is immunoprecipitated with messenger ribonucleic acidsencoding myelin basic protein, alpha calmodulin kinase II, and protamines 1 and 2

Testis brain RNA-binding protein (TB-RBP) is a sequence-dependent RNA-bindi ng protein that binds to conserved Y and H sequence elements present in man y brain and testis mRNAs. Using recombinant TB-RBP and a highly enriched tu bulin fraction, we demonstrate here that recombinant TB-RBP binds to microt ubules assembled in vitro. The interaction between recombinant TB-RBP and m icrotubules was inhibited by high salt and by the microtubule disassembling agents colcemid and calcium, but not by the microfilament-disassembling ag ent cytochalasin D. Confocal microscopy confirmed colocalization of TB-RBP and tubulin in the cytoplasm of male germ cells. An affinity-purified antib ody prepared against recombinant TB-RBP specifically precipitated mRNAs enc oding myelin basic protein and or calmodulin-dependent kinase II-two transp orted mRNAs, and protamines 1 and 2--two translationally regulated testicul ar mRNAs. These data indicate an intracellular association between TB-RBP a nd specific target mRNAs and suggest an involvement of TB-RBP in microtubul e-dependent mRNA transport in the cytoplasm of cells.