Minimum Requirements for the Function of Eukaryotic Translation Initiation Factor 2

Corresponding author: Ernest M. Hannig, Department of Molecular and Cell Biology, University of Texas at Dallas, Mailstop FO3.1, P.O. Box 830688, Richardson, TX 75083-0688., hannig{at}utdallas.edu (E-mail)

Communicating editor: M. HAMPSEY

Eukaryotic translation initiation factor 2 (eIF2) is a G protein heterotrimer required for GTP-dependent delivery of initiator tRNA to the ribosome. eIF2B, the nucleotide exchange factor for eIF2, is a heteropentamer that, in yeast, is encoded by four essential genes and one nonessential gene. We found that increased levels of wild-type eIF2, in the presence of sufficient levels of initiator tRNA, overcome the requirement for eIF2B in vivo. Consistent with bypassing eIF2B, these conditions also suppress the lethal effect of overexpressing the mammalian tumor suppressor PKR, an eIF2 kinase. The effects described are further enhanced in the presence of a mutation in the G protein () subunit of eIF2, gcd11-K250R, which mimics the function of eIF2B in vitro. Interestingly, the same conditions that bypass eIF2B also overcome the requirement for the normally essential eIF2 structural gene (SUI2). Our results suggest that the eIF2ß complex is capable of carrying out the essential function(s) of eIF2 in the absence of eIF2 and eIF2B and are consistent with the idea that the latter function primarily to regulate the level of eIF2·GTP·Met-tRNA_i^Met ternary complexes in vivo.

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