FIG. 8.

Internal cleavage of the initially cleaved prosequence is required for activation of Krp1. Krp1 mRNA and mRNAs from various Krp1 mutants that lack the normal basic motifs at either the primary or internal site were translated in Xenopus egg extract for 1 h in the presence of [³H]leucine. (Top) Samples were analyzed by SDS-PAGE on a high-percentage gel. (Bottom) Duplicate samples were treated in the same way except that cycloheximide was added after 1 h (to inhibit translation) and incubation was continued for a further 15 h before samples were analyzed. Mutant forms of Krp1 with stop codons introduced immediately after Arg102 (Krp1[R102*]), Arg99 (Krp1[R99*]), and Arg82 (Krp1[R82*]) were translated in extract to provide appropriate markers and aid in the interpretation of results.