Nuclear targeting of cAMP response element binding protein 2 (CREB2)

The transcription factor cAMP response element binding protein 2 (CREB2) be longs to a family of proteins containing a basic region as DNA-binding doma in and a leucine zipper as a dimerization domain in its C-terminus, Using i ndirect immunofluorescence labeling of cells we show that CREB2 is a nuclea r protein. To identify the signal(s) required for nuclear targeting of CREB 2, various domains of the protein were expressed in COS cells as fusion pro teins with glutathione S-transferase and their cellular location assayed by indirect immunofluorescence using antibodies directed against the glutathi one S-transferase moiety of the fusion proteins. The results show that the nuclear targeting signal is located in the C-terminal part of the molecule. Deletion mutagenesis revealed that the basic region of CREB2, encompassing amino acids 280 to 300, is sufficient for sorting CREB2 to the nucleus. Si ngle point mutations of basic amino acids within the basic region of CREB2 identified the sequence KKLKK (amino acids 280 to 284) as important for nuc lear targeting. Thus, the basic region of CREB2 is necessary not only for t ethering CREB2 to DNA but also for sorting CREB2 to the nucleus. However, s equences outside the basic region are additionally required for efficient n uclear sorting of CREB2.