Fig. 2. Maskin antibody activates the translation of CPE-containing mRNAs. (A) The salient 3′-UTR sequences of cyclin B1, Mos and Wee1 mRNAs are depicted (top); the CPEs (boxed) and polyadenylation hexanucleotides (ovals) are designated. Maskin antibody or IgG was injected into oocytes, which were then cultured overnight (no progesterone). Extracts were then prepared and three concentrations of protein were analyzed by western blots probed for cyclin B1, Mos, Wee1, MAP kinase and eIF4E. (B) In vitro synthesized CAT reporter RNAs that contained a 5′ cap (CAP CAT) or the EMCV IRES (IRES CAT) were appended with 3′-UTRs composed of either a polylinker sequence or a polylinker sequence harboring three repeated CPE sequences (3CPE) (de Moor and Richter, 1999). The RNAs were injected into oocytes followed by a second injection of IgG or maskin antibody; extracts were then prepared and CAT activity was assessed. Each experiment was performed five times. The bottom portion of the figure shows that injected maskin antibody, but not injected IgG, induced endogenous cyclin B1 synthesis in the same oocytes that were injected with the reporter RNAs.