Structure of the Beta Subunit of Translational Initiation Factor EIF-2

A human liver cDNA encoding the beta subunit of protein synthesis initiation factor 2 (eIF-2) was isolated and sequenced. The 1416 bp cDNA encodes a protein of 333 amino acids (38,404 daltons) with characteristics that resemble authentic purified eIF-2 beta. De novo synthesized eIF-2 beta from cDNA transcripts incorporates into endogenous rabbit eIF-2 complexes. The protein possesses putative GTP-binding sites, a zinc finger motif, and a highly charged N-terminal region composed of three basic polylysine blocks separated by acidic domains. The polylysine blocks and the zinc finger motif suggest that eIF-2 beta interacts with RNA. A yeast protein, Sui3, isolated as an extragenic suppressor of his4 initiation codon mutations, exhibits extensive sequence identity with human eIF-2 beta, especially in the polylysine and zinc finger domains, thereby reinforcing the view that these elements are important for function.