Stress-responsive eIF2α protein kinases. Consistent with its signal
transducing role, PKR responds to a variety of different stimuli,
including growth factor (GF), interleukin 3 (IL-3), tumor necrosis
factor α (TNF-α), and altered calcium (Ca2+) levels,
heat shock, and bacterial lipopolysaccharide (LPS). AA, amino acid;
dsRNA, double-stranded RNA; ER, endoplasmic reticulum. See text for
further details.