The κ promoter penta-decamer binding protein CBF-A interacts specifically with nucleophosmin in the nucleus only

CArG box-binding factor-A (CBF-A) interacts with the penta-decamer (pd) element that is a conserved sequence element within mouse Vκ promoters. The pd element acts in synergy with the octamer element to stimulate κ transcription, especially in later stages of B cell development. To get further insight in the mechanism for CBF-A action we have characterised its protein–protein interactions. We show here that CBF-A interacts specifically with nucleophosmin (NPM). This interaction occurs via the homo-oligomerisation domain of NPM and the N-terminus of CBF-A and was exclusive for the nuclear compartment while the two proteins failed to interact in the cytosol. In contrast, CBF-A formed homocomplexes in this compartment. CBF-A was also shown to localise to the nucleoli, most likely dependent on a functional interaction with NPM. Lastly, the sequence fine specificity of CBF-A complexes in the nucleus and cytoplasm were found to differ and nuclear protein–DNA complexes were shown to contain NPM. Thus, CBF-A participates in several protein–protein interactions that may modulate its subcellular localisation and target gene specificity.