FIG. 2.

Prosequence cleavage is autocatalytic. Krp1S371A or Krp1[IA82][KK102]S371A mRNA was translated in Xenopus egg extract for 1 h in the presence of [³H]leucine and was then mixed in the presence of 1% Triton X-100 with membrane extracts prepared from Xenopus oocytes that had been injected with either a control mRNA (lanes 2 and 5) or Krp1 mRNA (lanes 3 and 6). The digestion products were separated by SDS-PAGE. Lane 1 is included to aid interpretation. It contained the products obtained from a 1-h translation of Krp1 mRNA in egg extract; the products are proKrp1 (upper band) and Krp1 (lower band). Lane 4 was from a 1-h translation of Krp1[IA82][KK102] mRNA and demonstrates that the Lys-Lys102 motif at the primary cleavage site is cleaved in an active form of Krp1. The positions of molecular weight markers (in thousands) are shown on the left.