DIMERIZATION OF THE TESTIS BRAIN RNA-BINDING PROTEIN (TRANSLIN) IS MEDIATED THROUGH ITS C-TERMINUS AND IS REQUIRED FOR DNA-BINDING AND RNA-BINDING

Testis brain-RNA-binding protein (TB-RBP) is a single-stranded DNA- an d RNA-binding protein that is involved in chromosomal translocations, mRNA transport and translational regulation. Here we show from in vitr o and in vivo protein binding studies that TB-RBP dimers are the minim um structural unit needed for DNA- and RNA-binding. Truncation studies demonstrate that the C-terminus of 55 amino acids of TB-RBP is essent ial, but not sufficient for DNA- or RNA-binding, and deletion of the l eucine zipper motif in the C-terminus abolishes DNA- and RNA-binding. Changing cysteine 225 in the C-terminus to alanine does not significan tly reduce DNA- or RNA-binding, but reduces the stability of the dimer . We conclude that the leucine zipper motif is required to maintain tw o molecules of TB-RBP as a dimer which is stabilized by a disulfide bo nd involving cysteine 225.