TABLE 1.

Relative activities of various Krp1 mutants^a

Construct	Internal site	Primary site	Activity
Krp1	Lys-Arg	Lys-Arg	100
Krp1S371A	Lys-Arg	Lys-Arg	<1
Krp1[IA82][KK102]S371A	Ile-Ala	Lys-Lys	<1
Krp1[KA82][KR102]	Lys-Ala	Lys-Arg	1–10
Krp1[IA82][KR102]	Ile-Ala	Lys-Arg	1–10
Krp1[KR82][KK102]	Lys-Arg	Lys-Lys	>120
Krp1[KA82][KK102]	Lys-Ala	Lys-Lys	1–10
Krp1[IA82][KK102]	Ile-Ala	Lys-Lys	1–10
Krp1[KR82][KA102]	Lys-Arg	Lys-Ala	10–20
Krp1[KA82][KA102]	Lys-Ala	Lys-Ala	10–20
Krp1[IA82][KA102]	Ile-Ala	Lys-Ala	10–20
Krp1[W578*]	Lys-Arg	Lys-Arg	1–10
Krp1[S590*]	Lys-Arg	Lys-Arg	1–10
Krp1[Y611*]	Lys-Arg	Lys-Arg	80–90

^aVarious mRNAs were translated in Xenopus egg extract for 1 h in the presence of [³H]leucine. Cycloheximide was added (final concentration, 2 mM) to inhibit any further translation, and incubation was continued for 23 h to allow maturation to occur. Samples were analyzed by SDS-PAGE, and the amount of Krp1-related material in each sample was determined by using a PhosphorImager (Molecular Dynamics) with ImageQuant software (an allowance was made for the number of leucine residues in each construct). Equivalent amounts of protein were assayed for the ability to cleave the fluorogenic substrate Boc-Arg-Thr-Lys-Arg-MCA under initial rate conditions. The results are expressed relative to the activity of Krp1. Each sample was translated and assayed on at least three occasions, and each result was within the range indicated.