THE ASSOCIATION OF XENOPUS NUCLEAR FACTOR 7 WITH SUBCELLULAR STRUCTURES IS DEPENDENT UPON PHOSPHORYLATION AND SPECIFIC DOMAINS

The function of proteins is often regulated by their association with specific subcellular structures. Xenopus nuclear factor 7 (xnf7) is a putative transcription factor that is selectively retained in the cyto plasm from fertilization through the mid blastula transition (MBT). Cy toplasmic retention is dependent upon the presence of a aa-amino-acid cytoplasmic retention domain and the phosphorylation of two sites (sit e 1 and site 2) within the protein. We show that the N-terminal acidic domain of xnf7 transactivated a reporter gene in transfected cells, s upporting its function as a transcription factor. During mitosis xnf7: was associated with the mitotic spindle and chromosomes, while during the short embryonic interphase it was associated with structures at t he poles which were most likely centrosomes. The association with thes e structures was dependent upon the presence of protein domains and th e phosphorylation of a specific phosphorylation site (site 2). In addi tion, we determined that association with the spindle or centrosomes w as not necessary for cytoplasmic retention prior to the MBT. We sugges t that the association of xnf7 with these structures is due to its int eraction with other proteins that are colocalized. (C) 1994 Academic P ress, Inc.