Letter | Published:

A ribosomal protein mediates eIF-2 phosphorylation by interferon-induced kinase

Naturevolume 287pages6567 (1980) | Download Citation



We have previously reported that treatment of mouse L cells with interferon (IFN) induces a reduction of initiation factor (eIF-2) activity (ternary complex formation of eIF-2 with Met-tRNAf and GTP)1, and that the reduction of eIF-2 activity involves the phosphorylation of eIF-2 by an IFN-induced protein kinase2. In addition, we considered that the reduction of eIF-2 activity induced by the kinase (cyclic AMP-independent protein kinase) may be accompanied by the phosphorylation of some intermediary factor(s)2. This possibility was supported by early reports that at least two ribosomal proteins (of molecular weights (MWs) 35,000–38,000 and 64,000–67,000) of mouse L cells3–5 and cellular proteins of Ehrlich ascites tumour cells6 are highly phosphorylated by IFN treatment. Recently, we and others have purified IFN-induced protein kinases from different cells treated with IFN2,3,7–9. These purified kinases show several similarities. The reports suggested that the IFN-induced kinase may be responsible for the phosphorylation of the ribosomal proteins (MWs 35,000–38,000 and 65,000–67,000) and that the phosphorylation of these proteins by the kinase may be associated with the reduced eIF-2 activity in IFN-treated cells2–4,8,9. A similar inhibitory mechanism of eIF-2 activity has been demonstrated in rabbit reticulocyte lysates10–15. The present study was undertaken to purify a ribosomal protein [MW 65,000 (65K)] from mouse L cells and to examine the effect of the protein on eIF-2 activity, and also on the binding of the ternary complex to the 40S ribosomal subunit. We found that the eIF-2 activity was greatly reduced when both eIF-2 and the ribosomal protein were incubated with IFN-induced kinase in vitro. Available evidence suggests that the inhibitory mechanism of eIF-2 activity induced by the kinase in vitro may involve phosphorylation of the ribosomal proteins [a small subunit (MW 38,000) of eIF-2 and 65K ribosomal protein] by the IFN-induced kinase.

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  1. Samuel Baron: Department of Microbiology, University of Texas Medical Branch Galveston, Texas 77550


  1. Department of Bacteriology, Tohoku University School of Medicine, Sendai, 980, Japan

    • Kenzo Ohtsuki
    • , Masataka Nakamura
    • , Tsuneaki Koike
    • , Nakao Ishida
    •  & Samuel Baron


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