Isolation and distribution of elongation factor 2 in eggs and embryos of sea urchins

The subcellular distribution of elongation factor 2 (EF-2) in eggs and early embryos of the sea urchin, Strongylocentrotus purpuratus, was studied by employing the diphtheria toxin dependent ADP-ribosylation of EF-2. When egg and embryo homogenates were fractionated by sedimentation, EF-2 was found associated with a low-speed pellet containing yolk, nuclei, and mitochondria. It also sedimented at 80 S and 5 S. No significant amounts of EF-2 were found on polyribosomes. The 5S form of EF-2 probably represents a monomeric unit of the factor as EF-2 had a molecular weight of 95 000 on sodium dodecyl sulfate-polyacrylamide gels. EF-2 could only be isolated intact if soybean trypsin inhibitor or EGTA was present. The total amount of EF-2 was similar in eggs and embryos. However, the distributions of the factor between the various fractions were substantially different for eggs and embryos. Also, a marked difference in the physical association of EF-2 with material in the low-speed pellet occurred after fertilization. Specifically, in eggs, 23% of the EF-2 was associated with the low-speed pellet; in cleavage-stage embryos, only 11% of the EF-2 was associated with the pellet. In eggs, 65% of the EF-2 sedimented as 80 S; by the 16-cell stage, this amount decreased to 44%. Concomitantly, the amount of EF-2 in the 5S fraction increased from about 8% in eggs to 44% in the 16-cell embryos. In addition, Triton X-100 was required for the extraction of EF-2 from the low-speed pellet of eggs, but not of embryos.(ABSTRACT TRUNCATED AT 250 WORDS)