Mos-induced activation of p42MAPK does not inhibit DNA replication in Xenopus egg extracts. Buffer, Mos(KM), or Mos(WT) was added to CHX extracts and then incubated at room temperature for 40 min. Demembranated sperm nuclei (600 nuclei/μl) and [α-32P]dATP (0.2 μCi/μl) were added to each reaction, and samples taken at 0, 0.5, 1, and 2 h of incubation at room temperature. Samples were analyzed by electrophoresis on 0.8% agarose gels (see MATERIALS AND METHODS).