Model of the functional activities for the C-terminal fragment (CTF) of YB-1. In non-stressed cells full-length YB-1 protein is predominantly cytoplasmic and may shuttle between the nucleus and cytoplasm. In the nucleus, full-length YB-1 binds to the RE-1 element within the MMP-2 promotor and trans-activates gene transcription. Following genotoxic stress, full-length YB-1 is predominantly localized in the nuclear compartment. In addition, cleavage of full-length YB-1 protein by the 20S proteasome takes place; whether this occurs in the cytoplasm or nucleus has not been investigated. The cleaved C-terminal fragment (CTF) also resides within the nuclear compartment. Co-localization of full-length YB-1 and CTF in the nuclear compartment results in loss of transcriptional trans-regulation of the MMP-2 promoter. The MMP-2 promoter is transcriptionally activated by ectopically expressing CTF, that readily shuttles to the nucleus.