PROTEIN-SYNTHESIS IN RABBIT RETICULOCYTES-XXI - PURIFICATION AND PROPERTIES OF A PROTEIN FACTOR (CO-EIF-1) WHICH STIMULATES MET-TRANSFER-RNAF BINDING TO EIF-1

  • 1 January 1978
    • journal article
    • research article
    • Vol. 253  (17) , 6054-6059
Abstract
The peptide chain initiation factor, Co-EIF-1 was purified to homogeneity. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the homogeneous preparation gives a single protein band corresponding to a MW of approximately 20,000. In the crude preparation, Co-EIF-1 exists in 2 molecular forms: Co-EIF-1H (MW = 200,000) and Co-EIF-1L (MW = 20,000). Both forms are equally active in all the reactions studied. Upon heating, the heavy form (Co-EIF-1H) is completely converted into the light form (Co-EIF-1L). Radioactively labeled [14C]Co-EIF-1 was prepared by reductive alkylation using [14C]formaldehyde and borohydride. [14C]Methyl-Co-EIF-1 binds specifically to EIF-1; EIF-1.cntdot.[14C]Co-EIF-1 complex was analyzed by gel (Sephadex G-100) filtration. EIF-1.cntdot.Co-EIF-1 complex is distinctly more stable towards heat than EIF-1 alone and the quarternary complex, Met-tRNAf.cntdot.EIF-1.cntdot.Co-EIF-1.cntdot.GTP is more resistant to aurintricarboxylic acid than the ternary complex, Met-tRNAf.cntdot.EIF-1.cntdot.GTP. Both the quarternary complex, Met-tRNAf.cntdot.EIF-1.cntdot.Co-EIF-1.cntdot.GTP, and the ternary complex, Met-tRNAf.cntdot.EIF-1.cntdot.GTP, are equally sensitive to Mg2+ in the presence of EIF-2 (TDF). In the presence of Co-EIF-1, the initial rate of Met-tRNAf binding to 40 S ribosomes was significantly increased.

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