Identification of proteins of the 40 S ribosomal subunit involved in interaction with initiation factor eIF-2 in the quaternary initiation complex by means of monospecific antibodies.

Monospecific polyclonal antibodies against seven proteins of the 40 S subunit of rat liver ribosomes were used to identify ribosomal proteins involved in interaction with initiation factor eIF-2 in the quaternary initiation complex [eIF-2 X GMPPCP X [3H]Met-tRNAf X 40 S ribosomal subunit]. Dimeric immune complexes of 40 S subunits mediated by antibodies against ribosomal proteins S3a, S13/16, S19 and S24 were found to be unable to bind the ternary initiation complex [eIF-2 X GMPPCP X [3H]Met-tRNAf]. In contrast, 40 S dimers mediated by antibodies against proteins S2, S3 and S17 were found to bind the ternary complex. Therefore, from the ribosomal proteins tested, only proteins S3a, S13/16, S19 and S24 are concluded to be involved in eIF-2 binding to the 40 S subunit.