The Mapping of Interferon-Induced Proteins and Phosphoproteins from HeLa S3 Cells

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Abstract
Fourteen of 18 proteins induced by interferon-.alpha. (IFN-.alpha.) in HeLa S3 cells were labeled with [35S]methionine, resolved by two-dimensional electrophoresis, and assigned coordinates corresponding to HeLa proteins previously mapped by Bravo and Celis (Clin. Chem. 28, 766.sbd.781, 1982). Proteins phosphorylated with [.gamma.-32P]ATP in response to polyinosinic:polycytidylic acid [poly(I):poly(C)] were mapped similarly. Multiple phosphorylated species of a 72-kD protein were labeled in response to poly(I):poly(C) by extracts from IFN-treated cells but not by extracts from control cells. These are likely phosphorylated forms of the IFN-induced poly(I):poly(C)-dependent protein kinase, the enzyme responsible for the phosphorylation of the .alpha.-subunit of eukaryotic initiation factor 2 (eIF-2.alpha.). Two phosphorylated forms of eIF-2.alpha. were labeled in extracts of IFN-treated cells. One of these is a new phosphorylated product of the double-stranded (ds) RNA-activated protein kinase.