YB-1 protein spontaneously forms fragments and multimers. A. Recombinant affinity-purified YB-1 protein was subjected to gel electrophoresis and coomassie blue staining (lane 1, marker; lane 2, coomassie) revealing the spontaneous formation of signals at different sizes (1: 66 kDa, 2: ~50 kDa, 3: ~25 kDa, 4: 18 kDa). Lane 3 displays an immunoblot of the same recombinant protein preparation with T7-tag-antibody directed against the T7-tag at the N-terminus of the protein. B. Bands from electrophoresis of recombinant YB-1 protein (as shown in A) were excised and subjected to MS/MS analysis. The results of protein sequencing for the signals of interest (1-4) are shown.