The activity of oligonucleotides containing guanosine 5'-triphosphate in protein synthesis. I. The interaction of protein synthesis elongation factor I with cytidylyl (5'-3')-guanosine 5'-triphosphate.

The interaction of protein synthesis elongation factor 1 (EF-1) from wheat embryos and elongation factor Tu from Escherichia coli with cytidylyl(5'-3')guanosine 5'-triphosphate(pppGpC) has been studied. The dinucleotide 5'-triphosphate interacts strongly with EF-1 as evidenced by its capacity to inhibit the binding of [3H]GTP to the factor. The analogs pGpC and GpC do not interfere with GTP binding to EF-1 but guanosine 5'-triphosphate cyclic 2',3'-monophosphate and ppGpC are also potent inhibitors. The binding of the dinucleotide 5'-triphosphate to EF-1 was also demonstrated directly by the nitrocellulose retention method and by Sephadex G-50 fractionation using a radioactive analog iodinated with 125I in the 5 position of the cytosine of pppGpC. The dinucleotide triphosphate can replace GTP in the formation of a ternary complex EF-1-aminoacyl-tRNA-GTP and in its requirement for the binding of aminoacyl-tRNA to ribosomes catalyzed by EF-1. The absolute requirement for GTP in an in vitro polypeptide-synthesizing system can also be met by pppGpC and by guanosine 5'-triphosphate cyclic 5',3'-monophosphate. The bacterial factor EF-Tu differs drastically from eukaryotic EF-1 in its nucleotide specificity since EF-Tu only interacts slightly (if at all) with pppGpC. The low inhibition of [3H]GTP binding to EF-Tu by pppGpC could be due to a slight contamination in the latter compound.