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

Abstract

The functional properties of two forms of elongation factor 1 (EF‐1) from the brine shrimp, Artemia salina, were compared. The heavy form of the factor (EF‐1H) contains at least two different polypeptides and occurs in dried Artemia cysts. It showed little capacity to bind GTP to nitrocellulose filters (0.01 mol nucleotide/mol enzyme) and did not form a detectable complex with the nucleotide when subjected to gel filtration. No stable ternary complex between EF‐1H GTP and aminoacyl‐tRNA, was detected. EF‐1L; which appears during the development of the shrimp embryo, consists of a single polypeptide chain of 53000 molecular weight. It bound GTP effectively to filters (0.15 mol nucleotide/mol enzyme) and the complex formed was stable to gel filtration. EF‐1L formed a stable ternary complex with GTP and aminoacyl‐tRNA.Despite these marked differences, both enzymes were comparable in the following assays: (a) polyphenylalanine synthesis; (b) catalytic activity in attaching aminoacyl‐tRNA to ribosomes; (e) rate of attachment of aminoacyl‐tRNA to ribosomes; (d) ribosome‐dependent hydrolysis of [γ‐32P]GTP Furthermore, preincubation of EF‐1L with GTP and labelled aminoacyl‐tRNA gave no competitive advantage in binding the aminoacyl‐tRNA to ribosomes as compared to the same system without preincubation. These results suggested that ternary complex formation is not the ratelimiting step in the binding of aminoacyl‐tRNA to ribosomes.The possible role of the additional polypeptide components of EF‐1H in protein synthesis is discussed.