Fig. 6. (A) Typical blot of post-fertilization MPF and MAPK declines, as measured by Rb phosphorylation (upper two rows) and ELK-1 phosphorylation (lowest row), respectively. No decrease is observed in uninseminated metaphase-I-arrested controls. (B) MPF activity in 10 fertilization runs subjected to Rb phosphorylation assays. (C) MAPK activity decreases in fertilization runs assayed by phospho-ERK1/2 western blots ('P-MAPK', n=8) or ELK-1 phosphorylations ('P-ELK-1'; n=8). Bars indicate standard errors. pb1, typical onset of polar body 1 formation; pb2, typical onset of polar body 2 formation.