INTERACTION OF WHEAT-GERM TRANSLATION INITIATION FACTOR-II WITH GDP AND GTP

The wheat germ translation initiation factor 2 (WGeIF-2) was isolated in a homogeneous state by an efficient procedure and characterized. Its molecular mass, as determined by a gel-filtration method is approximately 150 000 Da. According to SDS-PAGE WGeIF-2 consists of four subunits with M(r) 37 000 (alpha), 40 000 (beta), 42 000 (gamma) and 52 000 (delta). The beta- and gamma-subunits (but not the alpha-subunit) of WGeIF-2 can be readily phosphorylated by the double-stranded RNA activated kinase isolated from rabbit reticulocytes. Dissociation constants for WGeIF-2 complexes with GDP and GTP were measured. In our evaluation the WGeIF-2 affinity for GDP (K(d)GDP = 1.5 x 10(-7) M) was only 10 times higher than for GTP (K(d)GTP = 1.5 x 10-6 M), While for rabbit reticulocyte eIF-2 (RReIF-2) the difference has been estimated as as much as two orders of magnitude in accordance with the literature. Close values of dissociation constants for WGeIF-2 complexes with guanine nucleotides suggest that at a sufficiently high [GTP]/[GDP] ratio the nucleotide exchange in wheat cells may take place without the participation of specific factor (eIF-2B) which catalyzes the nucleotide exchange on eIF-2 from mammalian cells.