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

Abstract

Fourteen of 18 proteins induced by interferon-α (IFN-α) 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, 766–781, 1982). Proteins phosphorylated with [γ-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 α-subunit of eukaryotic initiation factor 2 (eIF-2α). Two phosphorylated forms of eIF-2α 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.