Eukaryotic initiation factor 2 from rat liver: no apparent function for the beta-subunit in the formation of initiation complexes.
Eukaryotic protein synthesis initiation factor 2 (eIF-2) from rat liver has been resolved into two subfractions by anion-exchange chromatography on DEAE-cellulose. One of these contained all three components (eIF-2 alpha, eIF-2 beta, eIF-2 gamma) characteristic of mammalian eIF-2, whilst the other fraction contained only two. By a number of criteria these were shown to be eIF-2 alpha and eIF-2 gamma. The absence of eIF-2 beta from this fraction was not due to its proteolytic degradation during purification since it was unaffected by the inclusion of a range of proteinase inhibitors in the isolation media. The properties of eIF-2 containing or lacking eIF-2 beta have been directly compared. It was found that eIF-2 beta was not required for the binding of guanine nucleotides to eIF-2 or for formation of ternary initiation complexes with GTP and the initiator tRNA. eIF-2 lacking eIF-2 beta was able to form 40 S initiation complexes and the presence of eIF-2 beta was also unnecessary for the stimulation of eIF-2 activity by the recycling factor, eIF-2B. Some of these findings are at variance with previous reports in which eIF-2 beta was removed proteolytically. The role of eIF-2 beta in the overall physiological function of eIF-2 remains to be elucidated.
D000818:Animals; D002848:Chromatography, DEAE-Cellulose; D002852:Chromatography, Ion Exchange; D015852:Eukaryotic Initiation Factor-2; D008099:Liver / Q000378:metabolism*; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects*; D010448:Peptide Initiation Factors / Q000302:isolation & purification / Q000494:pharmacology*; D014176:Protein Biosynthesis; D011506:Proteins / Q000302:isolation & purification / Q000494:pharmacology*; D051381:Rats; D012156:Reticulocytes / Q000378:metabolism
D015852:Eukaryotic Initiation Factor-2; D010448:Peptide Initiation Factors; D011506:Proteins