RAF-1 IS ACTIVATED DURING MITOSIS

The Raf-1 serine/threonine kinase transmits proliferative and developm ental signals to downstream effecters in the mitogen-activated protein kinase cascade, Studies to date have concentrated on its role in grow th factor-mediated activation of the cell cycle. We show here that Raf -l kinase activity is also highly stimulated during mitosis, with an a ttendant distinctive electrophoretic mobility shift due to hyperphosph orylation. These results suggest that Raf-1 may play a role in travers al of at least two distinct phases of the cell cycle.