GTP interacts through its ribose and phosphate moieties with different subunits of the eukaryotic initiation factor eIF-2.

We have previously shown that a GTP derivative bearing p-azidoaniline at the gamma-phosphate group specifically labels the gamma-subunit of eukaryotic initiation factor eIF-2. In the present study a new GTP derivative carrying the photoreactive group at the ribose moiety of GTP was applied for affinity labeling of eIF-2 in different initiation complexes. Using this GTP analogue the beta-subunit of eIF-2 was found to be specifically labeled in all complexes investigated. It is concluded that GTP interacts with both the beta- and gamma-subunit of eIF-2: the guanosine moiety is in contact with the beta-subunit and the gamma-phosphate group with the gamma-subunit.