NUCLEAR CONCENTRATION AND MITOTIC DISPERSION OF THE ESSENTIAL CELL-CYCLE PROTEIN, P13(SUC1), EXAMINED IN LIVING CELLS

Stamen hair cells of Tradescantia virginiana have been microinjected with p13(suc1) labeled with carboxyfluorescein (CF) and studied throughout the division cycle in living cells by using the confocal laser scanning microscope. The protein, p13(suc1), is essential for the rapid inactivation of the key mitotic catalyst, p34(cdc2) kinase, at anaphase and for completion of nuclear division. During interphase or prophase, CF-p13(suc1) concentrates quickly (<2 min) in nuclei, reaching levels that are approximate to 2-fold greater than those in the cytoplasm. At nuclear envelope breakdown, CF-p13(suc1) permeates throughout the entire spindle and nonspindle cytoplasm. The protein is excluded from the tightly condensed chromosomes but otherwise no regions accumulate or exclude the protein. It remains evenly distributed throughout metaphase, anaphase, and well into cytokinesis; however, during telophase CF-p13(suc1) reconcentrates in the daughter nuclei.