Characterization of Developmentally Regulated Forms of Elongation Factor 1 in Artemia salina

Two forms of elongation factor 1 (EF‐1) have been purified from embryos of Artemia salina. A heavy form of the factor (EF‐1H) which is present exclusively in dried cysts, was found to contain three different polypeptide chains on the basis of electrophoresis in polyacrylamide gels containing dodecylsulphate: an A chain (Mr= 53000), a B chain (Mr= 51000) and a C chain (Mr= 26000). The holoenzyme elutes slightly ahead of beef liver catalase (Mr= 240000) on columns of Ultrogel ACA 34 and comigrates with catalase (s = 11 S) on sedimentation in a sucrose gradient. However, enzymically active more slowly sedimenting forms (8‐S and 5‐S) of EF‐1H, containing A, B and C chains were also observed. Gel filtration experiments confirm that the holoenzyme can readily dissociate into at least two lower‐molecular‐weight forms containing A, B and C chains. The C chain comprised approximately 30% of the mass of these different forms of EF‐1H. The light form of the factor, EF‐1L, which is exclusively present in hatched embryos (nauplii), was conveniently prepared from cysts which were developed for 6 h at 42°C. EF‐1L consists of a single basic polypeptide chain with a molecular weight of 53000 and a pl of about 8.3. EF‐1H also contained a basic polypeptide with an isoelectric point indistinguishable from EF‐IL. Further support for the presence of the EF‐1L polypeptide in EF‐1H was given by the weak but definite immunological crossreaction betweèn rabbit anti‐EF‐1L and EF‐1H. Based on the Mr of the subunits, gel filtration and sucrose density gradient behavior of the different forms of EF‐1H and the stoichiometry of the C polypeptide, a model of the enzyme is proposed in which the basic unit (Mr= 75000) consists of one A or B chain in combination with the C polypeptide. Although EF‐1L corresponds closely to a low‐molecular‐weight forni of EF‐1L prepared from pig liver, there is little similarity between Artemia EF‐1H and the heavy forms of EF‐1 from mammalian sources. The later have been found to consist of aggregates of a single polypeptide. On the other hand, there is a striking correspondence between Artemia EF‐1H and the heavy form of wheat embryo EF‐1 which also contains three different polypeptides. These similarities lead us to suggest that the additional polypeptides play an important role in maintaining the activity of EF‐1 during periods of biological dormancy.